I have used Daniel Defense, Stag, DPMS, Palmetto State Armory and G & R Tactical lpk's. The only one I wouldn't use again is the DPMS. It had some roll pin size issues and the quality just didn't seem quite as good. The G & R was probably the best quality although I ordered it without a trigger. The Palmetto one wasn't too bad and probably had the best trigger out of all. The DD lpk was pretty good, I would use one again. I did have a problem with the included grip screw not fitting, but a quick trip to the hardware store fixed that.