Ok, now I have asked a few people and this came from as different as "It will feel like a totally more accurate gun" to "no difference"

Well, i figured I would ask the guys who shoot them all the time, so I came here,

Ok, Im getting a Bushmaster, it will be used for mostly target and maybe cyote hunting at ranges to about 300yards max, because all my spots are short range, I want to build a tactical type rifle, "red dots, lights, ect...."
but I want it to be able to hunt too,

so, how much differene will i notice in the barrel lengths, and is 16 enough?

I'd go with a 20" A3 and have Kurt thin down the barrel under the handguards to USGI specs.

If your looking for tactical, go for the 16" barrel.  The accuracy is comparable to the 20", and it is a little lighter.  You don't want to be lugging a 20"er with the long A2 stock for a tactical situation, and the the 16" will be fine for both range and hunting.  Just get the A3 for a scope, or get the scope mount for the A2 handle.

16" is the best overall barrel length. For a tactical rifle the 16" is superior. That last 4 inches makes a big difference in handling in CQB environments. You don't see many SF operators or SWAT guys clearing houses with a 20".

Mostly target and yotes out to 300 is where a 20 is tactical.

well, this is my first time hunting cyotes, will 16 be good enough for cyote hunting be good enough? and would it be good to have the mini-y comp or nothing at all at the end of the barrel?

well, I read that fluting will make a better surface area and a stiffer barrel, this making it more accurate.

So, if I got a 16" barrel fluted, would it be as accurate as the 20'?

BUSHMASTER 20" A3 - quite possibly the best all-around AR15 made.

Go with the 20". It will have less recoil and be more accurate especially at longer ranges. If you put the y compensator on the 16" it will be super loud, I hear lots of complaints about this. It also sends a blast of air to the sides. For target shooting and coyote hunting you don't need to have the same mobility as the 16".

Add a scope and most all of the accuracy difference between 20" and 16" goes away.

Fluting a barrel does not stiffen it.  BUT, a larger diameter barrel that is fluted may be stiffer than a smaller diameter unfluted barrel of the same total weight.

The 20" barrels are smoother operating, no doubt about it.  But they are also clumsier around the house, in and out of transportation.

My personal preference is the 16".  I have only one 20" left, and that is a bull barreled, scoped rifle.  All my other AR's have 16" barrels now.

If the 16" is a mid-length from Armalite of RRA then it will be a bit more smooth in operation than the standard 16" gas system.

For target shooting and yote hunting I would suggest the 20" but the 16" will be fine for yotes, butI wouldn't go past 300yds. I have two uppers, a 20" for target and hunting and a carbine for the house.

For the type of coyote hunting I do, I want the shorter barrel. We call in close cover and a long rifle is a real PITA. I actually prefer a handgun, but a short AR would be my next choice. The other mode of hunting is spotlighting from a truck. Again, the shorter barrel is much easier to handle in the truck and when getting in and out of the truck.

In fact, my main, go-to AR is perfect for the type of hunting I do; 16", dot sight.

If I was calling in open country where shots are closer to the 300 yard mark, I would go with the 20". It will give you more velocity. Accuracy is the same with either barrel length.

Fluting DOES NOT stiffen a barrel. If you have two barrels of the same diameter and one is fluted, the fluted one will be LIGHTER, but the solid barrel will be STIFFER. One benefit to fluting is that is does give more surface area, and therefore the barrel will cool down more quickly after a rapid-fire session.

For the type of shooting you want to do, I'd recommend the 20" barrel. If you want to get a fluted barrel, do so, but don't expect it to spit out 'magic bullets' like the marketing a-holes would have you believe.

The 20" barrel will have a higher muzzle velocity than a 16. This is important in long-range varmint hunting. 300 yards is a LONG shot at a varmint IMHO. I'm not saying it can't be done, but with a .223 I try to keep my shots under 200-250 yards to ensure clean, humane kills. My rifles are plenty accurate enough to shoot beyond that range, but the bullet velocity drops WAY off after 200 yards, and bullet performance becomes an issue. If I'm going to be shooting at long-range yotes, I use at least a .22-250.

Ultimately you have to decide what's right for you. And if you're like most of us, you'll end up with several uppers in different configurations for different situations.

Well, is it easy to get cyotes within 200 yards?
If so then I want the 16in., I will be mounting a Aimpoint M2 after i learn the Open sights well., Besides the longest range where i live is only a 100 yard range.

I think I will get another upper though, It will probably be for accuracy, this 16 will be for fun and occasional hunts,

What else is huntable with an ar-15?

Prairie dogs are a blast. No pun intended. I also like to shoot crows.  

If this AR disease really hits you and you go custom for that second upper, consider an 18" barrel.  That length is (IMHO) the best to achieve adequate velocity and is still very handy.  (ArmaLite had figured out by 1963 and the AR-18 that you could get 3100fps+ out of an 18.25" barrel - 1:12 twist and 55grn bullet.)