These guns all have their following and each has a proven track record.
DPMS in my opinion makes and excelent rifle at any price point. I have than A2 M4 and it is flawless everything I feed it.
But I also clean my guns and don't dump 1,000 rounds at a time down range.
(When Wolf ammo is shot alot and the gun get very hot the Wolf Steel case may expand and fail to eject. Steel casings are a pain to remove. Brass not so much.)
Do the research (Here, GlockTalk.com under BlackRifle and AR15.com) Read what real user are shooting, the ammo they like and then test fire a few. (Here in Vegas three places rent several models)
I already had done the leg work and was shopping for an $800 bone-stock M4 when I found a great deal on my DPMS. (Dealers here sell one model of DPMS for $700, but they are never in stock)
If I had found one of the other (ABC) at that sub $800 price point first, I would have bought it. But I got lucky and found my 16in barrel, M4 A2 flatop with handle, in a hard case, 2-30rds mags, cleaning kit, bore sighter, all in pristine condition for $600. (That's not a typo)
Get the cash together, be patient and start looking.
As for accuracy my 16in barrel has a 1 in 7 twist. These M4 prefer 60 to 75 grn bullets for best accuracy.
At 100 yards with 55grn UMC bullets (25 cent each) I get 2 to 3 inch groups, open sights. With Wolf 62grns (50 cents each) Sub 2" groups.
I just ordered some 75 grn (85 cents each) match ammo. I've been told it will do 1 to 1.5inch groups or better with the right M4.
I also put a 6x scope on mine (I have 4x16x40 on order) and I have 10- 30 rd mags coming this week with 6 kinds of ammo. Test, Test, Test......
Once I'm done at 100m, I'll need to move to 400m and see what happens.
If you want to shoot the cheap ammo like the Wolf 55 grn all the time, best accuracy for those is usally a 20 barrel with 1 in 9 or 1 in 12 twist.
The original M16 I shot in my early military days all did really well on the cheap 55grn goverment ammo.
Later, the military moved to 62grn bullets for the smaller barreled M4. Seems to work really well in the Sandbox for our troops right now.