This guy covers it all. http://forums.officer.com/showthread.php?t=81462
A litlle tip on what to avoid, Hesse Arms out of business due to shotty workmanship. DPMS is known for having tight chambers that will not feed all ammo.
I like Stag. But to each his own. None are really bad. I would suggest you get at least a 1-8 barrel so you can get into the 75 grain bullets if you ever desire. I have a 1-7". The recent push in heavy bullets has been phenonamal for the ar. But that's another thread.
Good luck