Good or bad individual experiences aside, DPMS is a bottom feeder in the AR15 world. They make a product with some of the worst quality control out there. Parts that are out of spec and would be discarded by companies like Colt and BCM are used by DPMS.
Now does this mean all DPMS rifles stink? No, they make a bazillion of them so I'm sure there are lots of happy DPMS owners out there. The problem is that a much higher percentage of turds make it out of the factory than with other makers.
The very top shelf AR makers are (in no particular order):
Colt
Daniel Defense
BCM (Bravo Company)
Noveske (IMO super top shelf)
KAC (super top as well)
Centurion
LMT
Colt
I'm sure there are a few others I've missed. You'll notice I put colt on the list twice. That's because a list of "fighting" ARs begins and ends with Colt.
Now about Rock River, RRA is a company that uses some non-milspec parts and that earns them a middle to lower end reputation for quality of build. RRA is always rated very high in accuracy though and they tend to specialize in building accurate ARs instead of "fighting" ARs. If you are looking for a long distance AR then Rock river is a good place to start. Just know that RRA rifles are made with accuracy in mind, not longevity.
My favorite AR maker is BCM. I've had a couple of them including one of these:
BCM SS410™ 18" Rifle Length Upper Receiver Group w/ VTAC ALPHA 13" Handguard 1/8 Twist
^^^^ If you are looking for an accurate AR upper look hard at one of these. Mine consistently shot 1/4 MOA at 100 yards with 69gr SMKs.