The best way to go for an AR, is to buy the assembled upper you want, buy the lower you want, buy the BCG you want, buy the fire control group you want, buy the stock you want, then put it all together yourself. It's very fun, very easy, requires almost no tools, and will give you better knowledge on how it all works and comes apart for future cleaning and upgrades.
All you need to do, is research what brand for each peice you prefer, and where the best place is to buy those pieces. I recommend ar15.com as a hang out. I hung out there for a couple months before finally pulling the trigger (no pun) on all my parts for my latest AR build.