I had the "itch" a year ago and just bought mine. After doing the research you're now doing, I ended up with the Rock River Arms Tactical Entry. RRA comes with the 2 stage trigger and match barrel for 1100. Once you add a new trigger and barrell to the DPMS, Bushmaster, or S&W, you're in the $1,500 range. Most of the gunsmiths and shops I spoke with favored Rock River for gas operated AR15. LWRC was the top recommended AR for piston systems (I don't need to shoot underwater).
Out to 200 yards it is as accurate as my Rem 700 bolt actions @1 MOA. opens up from there. I'm very happy with RRA.
Get yourself PMAGs to replace the factory magazines. PMAGs are the best. I also highly recommend the Lula mag loader.