Looking at building my first AR. I bought a fully assembled AR15 from PSA a couple years ago and really like it but want to try my hand at starting from scratch. The gun I have is more of a home defense as it is a short barrel pistol AR. Looking for suggestions on what to build. Want to build something I can take in the deer woods and have a different option that what I have. .300 blackout? 6.5? AR10? Somebody school me.

For a capable deer pistol I'd suggest a 12.5" 6.5 Grendel. Mine gets 2,340fps from a 123 SST. Has >1,000ftlb of energy out to 250 yards.

Hard to go wrong with a Grendel build, how long, that's up to you. 300 blackout works good too(super and sub).

What distance do you anticipate shooting?

Assembling one will(well, should) require a few tools to make the job easier. If you have any mechanical ability, it'll be easy. Hardest part might be what all brands of all the parts to buy and how much you want to spend. I've used parts from numerous suppliers/brands, they've all always assembled mix/matched fine save for one take down pin, which was out of spec.

If you're planning to use it on deer, I'd look into the 6.5 grendel.  223 & 5.56 have taken plenty, but the 6.5 grendel has a lot more to offer.  The 300blk has as well, but it really doesn't compare to the 6.5gr.  Just look over the ballistics and make your choice.

I would not look at anything in the ar10 types just due to weight and the fact that it's not as standardized as the ar15.  I like the ar10, but it's kind of a tank when compared to the ar15.  Compare 6.5 grendel to the 308.  Yes, the ar10 can support the 6.5 creedmoor, which adds additional "wanna" to it.  And the 300blk has very similar everything to the 30-30.  You could also look at the 6.8spc, and a few others as well.  If going to the ar10, there are many other options additionally.

Having done it, I'd choose 6.5 grendel over 300blk for normal use.  If planning to suppress it, then I'd maybe look more closely at the 300blk.  But, my choice would be 6.5 grendel, 18", rifle length, no muzzle device, and a low to mid-power variable optic.  Vertical grip on the lower, single stage trigger, and a shorter fixed stock.

Lots more options, too.  What are your hunting conditions?  What else do you want to do with it?  Are you planning a rifle or a pistol?  What are the weather conditions you need to deal with?  Do you walk a lot, or do you sit in a stand?

For deer you might wanna take a look at the 350 Legend.

Planning on building a rifle. Would be sitting in a stand 99% of the time. Would do some target shooting with it but mostly just a fun gun that I can hunt with. I hunt in SC/GA so the weather conditions don't get too bad.

Any advice on what specific tools I might need to make it easier on myself?

What is your idea of building and AR15. Assembling? Pinning a gas block? Completing an 80% lower?

For basic AR15 assembling of basic parts from a stripped lower/upper:
Torque wrench if you are using a non-indexed barrel nut. Standard barrel nuts and those that rely on the position of the gastube are indexed barrel nuts and don't require to be torqued down to a specific value. Position of the gastube thru slot becomes important, but there is a specific procedure to know how to do it correctly.
Geiselle Reaction Rod, Magpul BEV Block, upper receiver clamshell or a tool that will hold the upper in position whiel you install a barrel nut.
Barrel nut wrench - some manufacturers use proprietary barrel nuts and have their own tool. Most AR15 barrel nut wrenches are for standard GI/Milspec barrel nuts/delta rings assemblies.
A lower receiver vice block (Magpul BEV works like this as well) or Geisselle Reaction Block to hold the lower receiver while you torque down the castle nut
Castle nut wrench - A lot of AR15 multi-tools are milspec barrel nut wrenches and castle nut wrench combos.
Wrench to tighten down muzzle device
Allen keys to tighten down LP gasblocks or various accessories. Some pistol grips use Hex head bolts, vs some use Flathead screws.
Bench vice for holding down everything
Pin punch set
Roll pin punches, you can specifically also purchase a dedicated bolt catch roll pin punch to help prevent scratching the lower.
I have a Geisselle gas block rollpin starter and punch set. Makes for getting those tiny pins in easier.
Gasblock fixture for holding the gasblock even on a table.
Molydenum Grease for the barrel nut/upper receiver threads, specifically Aeroshell 33MS. A full tube will last a lifetime. A little bit goes a long way.

*If ou are building an AR10/SR25 platform, you will need some other specialty tools like a different upper receiver vice block/barrel extension vice adapter. Magwell block etc.
**Also have spare small parts. If its your first time assembling a lower, you are almost guaranteed to loose a takedown pin spring or detent.

I personally like to dimple barrels getting LP gas blocks. A dimpling jig if that is what you want to do. It helps ensure that gasblock is aligned to the gas port. Not all barrels have dimples, so I have a jig for those that don't.
I also like to pin my LP gasblocks. So a LP gasblock pinning jig is also in my inventory along with carbide drill bits to get through nitride parts.  I use BRD for both dimpling jigs and Pinning jigs.
If you want to stake the endplate/castlenut, you'll need a center punch tool and hammer.
I check headspace for all nonmatching bolts and barrels, so a bolt ejector tool so I can remove the ejector. Plus headspace gauges.

Someone posted this the other day. Idk if you could shop around and but pieces cheaper.

https://www.ar15.com/forums/AR-15/New-builders-just-buy-this-already-Tools-Good-Cheap-/4-747050/

I like a lower assembly block as well. A good set of hex keys(sae). Roll pin starter punches.

I would like to suppress the rifle build which seems like the .300 blk is a better option. Most of the ones I have seen are shorter barrels. Can you run a longer barrel suppressed with the .300 blk and still get the same performance? Can the 6.5 be suppressed? Extreme novice here so excuse my questions.

Short barrels in 300 BO and heavy bullets keep the MV sub-sonic which results in the relatively quiet report.  The 6.5 will be super-sonic.  A longer barrel in 300 will increase the MV and likely go super.  You can suppress it, but it will be much louder than a sub-sonic 300

300blk is less than half the energy you get from 6.5 grendel so it isn't a GREAT hunting round. You're <500ftlb in less than 200 yards with 220s, and never get even 500 with lighter than that. Basically hits like a 45acp. In fact, might as well build a 45acp instead, the ammo is far cheaper. Supersonic 300blk doesn't add much -- about 300ftlb in my (very short) rifle, still never gets to 1,000.

The 6.5 is going to have the same energy at 600yd that the 300 sub has AT THE MUZZLE. Much better hunting round. You need to decide which one you want.

The only downside to a supersonic round (6.5 or 300blk) is the supersonic crack, and that's going to be the case with any round you likely want to hunt with. No difference there except the 300 can shoot subs better than the Grendel.

While your points are valid I personally know a guy with over 300 deer kills from near to over 400 yards with a subsonic 300 and a suppressor, shooting 220's.  He does deer culls near population and needs to be quiet.  He is a pro, however.  He knows his drops and compensates accordingly with his optic.  He also does autopsies on the kills.  The bullet tumbles upon impact and destroys the vitals.  They seldom move after the shot, usually give a twitch like getting stung by a bee and then drop dead.  Just saying, it can be done, but there aren't many with the skill to do so.

He's a very good shooter with a special circumstance. If he had the option I bet he'd use supers. A subsonic 220 is dropping one inch every yard by the time it hits 300yd, and almost 1.5 inches per yard by 400. You definitely need to know your holds and have a good rangefinder -- being off by 5 yards is is likely putting you out of the vitals.

Oh, he uses the big guns when he can.  His favorite is the 6.5/284, has over 2100 deer kills under his belt.

Getting ready to order the lower. Options at the local FFL are Aero, Anderson, and Spikes. Obviously there is a big price gap in Spikes and the other two. I've read the stripped lower isn't extremely critical and might be an item that you can save some money on. Is this true? Anyone have any recommendations or experience with these three? Not too worried about the money difference. Want something quality, but I won't be shooting the gun all the time either.

Few differences. I have all three and they are all fine.

Of the three I'd probably prefer the Aero -- they make great stuff all around.

You've got 2 separate ideas going on here.  300blk was designed for use in a short barrel.  Go subsonic to get things really quiet. You can suppress the 6.5, but I don't think you'll be able to find or make subsonic ammo for it - although there's probably a way.

If you want both of those things, I would suggest building 2 separate rifles, or preferably a SBR or pistol in 300blk.

Of those three, I'd go for Aero.  My understanding is that Aero make the Spikes lowers, although that could have changed.  Also think you will be hard pressed to find anyone complain about the Spikes.  Given the choice between Aero and Anderson, I'd take Aero every time.  Also Aero is getting better about offering different variations, which is nice, and most of their lowers that you can find floating around are Gen 2, so they have an adjustable compression screw at the rear takedown pin so you can adjust away receiver rattle.  If you can find an upper & lower set from Aero, then even better.

Given the choice between Anderson and Spike's, I'd probably go with Spike's.  Plenty of people happy with their Anderson stuff, they've had QC problems in the past, but every manufacturer that produces high volumes will.  But will still go Spike's.

No reason a subsonic 6.5G load couldn't be made. Might not cycle the action, but at that point you are throwing a 147gr projectile at the speed of sound, which sounds a lot like a 9mm.

Much as 300blk slinging a 220gr projectile at the speed of sound sounds like a 45acp. Better ballistics on both, but the energy is the same and the ammo would be much more expensive than the corresponding pistol ammo.

If you go with the .300, be prepared to get anal about keeping ammo and mags separated...if a .300 BO round makes its way into a .223 or 5.56 chamber (it will fit right in there) and the trigger is pulled, bad things happen...kaboom.
Not trying to dissuade anyone on the caliber, I have one and love it, but it does introduce some risk when you take both guns/calibers to the range. Not a huge deal if you are careful, but it's worth a moment of consideration.
I either take one or the other out and not both, or I shoot one first and pack up all the ammo and mags before breaking the other caliber out. Having both guns and ammo types out at the same time is a red flag for me.

I’m also very careful when it comes to keeping the 5.56 and 300 separate. All 300 mags are labeled. I also shoot only 1 at a time. I never put the both on the bench at the same time. I shoot the 300 first, then pack it up and finish off with the 5.56
I love the 300, but shooting can be very pricey per round. Cheapest I found was Palmetto’s freedom bucket; 160 rounds for $80 shipped

I agree.  Have built on several lowers and if given the choice, Aero is my prefered.

Agreed I think you could make a 6.5 subsonic, but you won't get the advantage that the 300 has with 220's.  That loooong bullet is barely stabel in flight and once it hits skin and flesh it tumbles and tears up the innerds of a deer.  Energy isn't a factor so we shouldn't get hung up on that and the 300.  You can also run the 300 supersonic with 110's and it kills that way as well, but not nearly as powerful as a 6.5 nor as good of downrange ballistics.  If going to run suppressed, the 300 would be the ticket.  The 45 Super would be another valid option for close range, suppressed.

Is it necessary to get a matching set as far as upper and lowers go? I have done some research and some people tend to talk about a little play between them if they are not bought as a set or from the same manufacturer. Narrowed it down to Aero or Spikes lower. I'm leaning towards the Spikes just due to some of the customization options on the lower with logos etc.

Yep. All my mags are dedicated to a caliber and marked, and a mag band around the handguard to mark each upper to avoid any mistakes. It is pricey to shoot but I enjoy it more than the 5.56, the bigger bullet gives much better target reaction. Beer cans fly, rocks break, steel rings nice and loud. Looking forward to Wolf steel-case ammo at less than half the going price, should be a game changer to the current ammo market for this caliber.

Fit can be an issue, but moreso might be the color of the ano if you are anal about things like that, which I am.  I had to paint one lower becasue the color was so off.

Just ordered this kit that was suggested in another topic along with some bolt catch pin punches. Getting ready to hopefully make a decision on a lower and get started on my first build! Appreciate all the advice so far.

https://www.midsouthshooterssupply.com/item/00350arsmith5/ar-15-ultimate-gunsmith-builder-set-(upper-and-lower-vise-block-and-ar-15-wrench-and-8-piece-pin-set)

Decided to go with the 6.5 grendel build. I've got a Spikes Tactical lower coming in the next couple of days hopefully. Looking at LPK's. Where is a good place to look for deals? What do I need specifically for a 6.5 build other than the barrel and the BCG? First timer. Looking forward to getting started soon!

Mags are it. The ones from Alexander arms work well.

Finally was able to get started working on the build. Got most of the lower put together. I got an LPK without the trigger assembly so I've got to get that next to finish it up. I was trying to post a picture to show my progress but I can't for the life of me figure out how to do that.