Dude! Which one? We had a pile of rifles when we were all out there last November.
Seriously though (kinda). As others have said, pretty much different rifles for different situation/purposes.
As an example:
A suppressed 300 BLK SBR for short range "quiet" work. A very effective, and scary Hollywood quiet, weapon for short to mid-range area clearing/securing.
A Daniels MK18 SBR. A DAMN fine and proven weapon for kicking in doors and clearing smaller confined areas. Coupled with the ability to still stretch out to medium range targets with some pretty good accuracy.
An Armalite AR-10 SBR. Screw kicking in the door. Just shoot right through it....or the wall next to it......and the wall on the other side of the room. Still very maneuverable, and still pretty accurate for medium range work as well.
An Armalite AR-10 SASS. Capable of being suppressed, and VERY capable of long range work.
This is just a handful of different configurations that can be built (or bought), but have very different applications. It all depends on what an individual plans to do with said rifle. As Edgecrusher pointed out, Different work calls for different configurations. And with the crowd that we have around here, we pretty much cover all of the bases for different configs and purposes of AR's, large frame or the smaller AR-15 frame. Along with many different calibers.