I have the Colt MT6601 post ban. I have been very pleased with it. I have always been confused with those who tend to speak negatively of Colt's fit and finish. It's possible that bad ones get through once in a while, but I've also seen posts of those who have sent it back for refinishing and Colt has been very helpful.
The Colt 6601 is fun to shoot - it's also a lot of fun to bring my friends with me. They love to shoot the real "army rifle" ;-) I have found the 6601 to be very accurate too.
I find the MT6601 to be a very good basic AR. Shoots nice and I believe it is well built. This was my entry into ARs, and it's caused me to get into a lot deeper. I can't say that I won't purchase any other brand (Bushmaster is another strong vote) at some point, but I tend to look at Colts first - the pre-bans now are receiving my attention as well as the new Colt 6400C carbine.
Hope that helps,