2nd for Bravo Company.
http://www.bravocompanyusa.com/ Their BCM brand is top notch. I also highly recommend PK Firearms
http://www.pkfirearms.com/, and I like their Sabre Defence line. They also carry Noveske if you want to go all the way to the top.
I have a lot of RRA stuff and I really like it. Bought it all from Adco Firearms
http://www.adcofirearms.com/, and they are my go to AR15 machinist and gunsmith if I just can't figure out a way to do it myself.
I would suggest you build up your own lower with the trigger you prefer, and purchase a complete upper. Best Lower parts kits are RRA, Stag. DPMS kits are fair quality at least the 1 I have used.
I recommend an RRA match 2 stage trigger at the minimum, and the Geissele SSA 2 stage would be my best recommendation.
I highly recommend Magpul stocks, grips and accessories I use CTR's on all 3 of mine and Magpul Pmag magazines. I recommend the mil spec extension tube as you have more choices that way.
Best Lower parts kits are RRA, Stag. DPMS kits are fair quality at least the 1 I have used.