Micro, The DI system is fine. If your looking for something for combat or just like to pay more buy a piston.
I own 2 of DI, one is a RRA 5.56 and the other I built off a RRA upper and lower in 6.8 SPC. Both of these guns are a whoot to shoot. Extremely accurate and reliable.
I've put over 500 rds out of mine with never touching it in the 5.56. You do have to clean a DI system more, but not enough to where its really going to make a difference on a weekend shooter.
If you really want a Piston gun buy a FN Scar. The AR isnt a piston gun, its been monkied with to make it work.
S&W makes a fine AR, So does RRA, Bushmaster, and a bunch more companies.
Larue, LMT, Noveskie, Les Baur and a couple others are the primo.