Kind of a late post on the thread, but to answer the question you asked. I personally would rate for quality, fit, and function:

1 Bushmaster
2 Colt
3 Smith and Wesson
4 Olympic Arms
5 DPMS

I have owned several of all of them except the S&W(I have a personal grudge against S&W stemming from the 90's and the assault weapon ban.) The Bushy's and Colt's finishes match up better with more uppers I think.