I'm starting to piece together a new AR(to replace the one I sold a while back) This build is going to be a M4gery.

I'm debating if I should go with a A2 style upper or go with a flat top. I'm not going to have any optics right away but I hope to add some later on(much later ).

What say the hivemind?

Just for the fact of later you plan on adding optics I say A3

A3 and a cheap rear sight.  Like the ones cut from an old carry handle.  A2 and A3 are both about the same price up front, but when you go to mount an optic later, it is allot easier and looks nicer on an A3.

A2's are slowly fading away because they lack the veratility of the A3.

Quoted: Just for the fact of later you plan on adding optics I say A3

But that means I have to invest another 100 bucks for iron sights until I get some optics.

What's the disadvantage of putting a scope mount on the carry handle?

Well,  by definition if it's gonna be an M4gery, then it should be a flat top.

I've assembled about a half dozen ARs for friends and I always lean them toward a flat top.    Much, much more flexible later on when you decide on an optic.

Get yourself a nice BUIS and learn to shoot with those irons.  When you finally get an optic, the BUIS will be second nature to you.

Here is an example of what I'd recommend;

 

This one really is a no-brainer:

Go with the A3 flattop, with removable carry-handle.  (I believe Bushmaster, Colt, CMMG, and RRA are all making them). That way, you can use the irons for now (and that's really not much of a "step down" anyway), and then once you have saved up for optics, just pop off the carry handle, and you have the correct platform for mounting of those.....oh...and... then you will buy Night Vision Devices, too, because you are so afflicted with BRD and acceserosis.

This is MUCH easier than having to send your upper to Bushmaster, when you buy the A3 receiver later, after you realize that A2 carry handles are terrible places to which to mount optics.  I just sent them my XM-177 today, since I wasn't sage enough to foresee this when I bought it 15 years ago.

Quoted: Quoted: Just for the fact of later you plan on adding optics I say A3 But that means I have to invest another 100 bucks for iron sights until I get some optics. What's the disadvantage of putting a scope mount on the carry handle?

It is not $100 when you subtract the extra cost of buying an A2 upper versus the cheaper A3.

The disadvantages I found with scopes on my A2s were;

1.  Too tall . . . it had a terribly uncomfortable cheek weld.

2.  The required A2 carry handle mount has a hole drilled in it so you can still use your iron sights.  This hole created a "tunnel vision" effect when I used my irons.  I felt like I was shooting in the dark when I used my irons while looking through the scope mount.

This pic is pretty much what I was recomending.  Also, get a good pistol grip.  I like the ergo grip personally, but there are many good ones.  One of the cheaper upgrades you can do that has make the rifle feel so much better and look better too.

I bought an a2 years ago, and wished I had bought an A3.  I finally picked up a flattop

+ 1 on the problems scope mounting on carry handle.....Don't do what I did

The optic is much too far above the bore.

Thus, the trajectory of the bullet is more difficult to discern using that setup.  For example, if the EO (in this pic) is 3.5 inches above the bore, then the POI will be very low at 25 yards, and very high at 100.  How do you know where to hold?  I would sometimes see the POI 2" low @ 50, and then 5 inches high @ 100.  This defeats the purpose of having a flat shooting cartridge like the 5.56.

When the bullet exits the muzzle, it must rise to the line of sight.  Once it crosses the line of sight, this is called "zero" and more appropriately "maximum point blank range."  This is the range at which your bullet is minimally divergent from the line of sight.  So, if the MPBR of a .223 with scope 1.5" above the bore, is 136 yards, then you can simply zero the rifle at that range, and the bullet will never be more than 2" away from the line of sight, until you get out to about 300 yards.  Placing the scope twice that high, changes the MPBR resulting in strange amounts of hold-over or hold-under at what are the most common ranges where we shoot.

Bottom line:  GET THE FLATTOP!

Quoted: But that means I have to invest another 100 bucks for iron sights until I get some optics. What's the disadvantage of putting a scope mount on the carry handle?

It all depends on what you want to do with the rifle and what type of optics you are going to use.  If you want to use a magnified optic/scope then a flat top will probably make the most sense because you can mount the scope lower.  If you are going to use a red dot you can use a goose neck type mount, like the ARMS #39, and cowittness the iron sights.  You can mount an optic on the carry handle, but some do not like how high above the bore it puts the optic.

I bought my A2 carbine a few years ago and decided to go with the A2 since I would not need to buy a BUIS.  I also purchased an ARMS #39 so I could mount an Aimpoint low, behind the front sight.  Since then I have decided that a flat top upper would now be a better choice and in the next month I plan to replace the A2 and ARMS mount with an A3 and a free float handguard.  I will also have to buy a BUIS.

In the end the choice is yours and just depends on how you want to use your rifle.

Sarge

Get an A3 with an rear BUIS.  Sure the BUIS cost another $80 - $120 but that is partly offset by the fact a complete A3 is $50 less than a complete A2 receiver.

You don't need to spend 80 bucks on a back up sight.  There are cheaper ones out there.  They may not be the best, but they will get you by unil you can get something better.  Chech out Cheaper than dirt or Aim surplus.

The equipment exchange also has them allong with detachable carry handles fairly cheap if you keep looking.