I don't have an axe to grind, but I recently received a 6920 (LEO order) and it was certainly shoddy. The lower receiver had nasty, deep "pitting" on the outer surface (forging defects). The Parkerizing on the barrel was spotty with areas of bare steel showing through. The flash suppressor was no aligned correctly. The feed ramp cuts were far from smooth: they had significant tool mark grooves left in them.
I've also seen/used some excellent Colt carbines (we have several where I work), but I'm concerned that QC may have taken a dip from what I'm accustomed to from Colt. I sent this one to Colt immediately upon receipt, hopefully they'll do me right.
urmynv: I don't see how you could possibly purchase a 6921 (legally). I guess the best bet would be to get a 6920 (will be hard to to 6 mo's from now), and have the barrel switched to a 14.5. I don't think the A2 flash suppressor will get you to 16", you'll have to get the longer Phantom or Vortex FS pinned on. You can also order a Bushmaster with a 14.5 and a Phantom already attached. I don't think it will have the M4 feed ramps, however.