People love to hate on DPMS, but mine runs great. Maybe I got lucky. Mind you, I did buy it before I knew anything about AR rifles, and I think the above advice has been good. Since I have heard mixed reviews of DPMS, Bushmaster, Armalite, Olympic, etc... given the choice to do over, I would probably pick a brand with a more "spotless" reputation.
My reading of history convinces me that most bad government results from too much government.~ Thomas Jefferson