Fullautoglock, if you really must buy a pre-ban AR-15 right now, Colt would be my first choice, then a factory-assembled Bushmaster with letter of authenticity as my second choice. All Colts made before the ban left the factory as complete rifles, so there is no need to prove their assembled state before the ban. Bushmaster sold both complete rifles and separate lowers before the ban. An AR-15 rifle had to be complete before 9/13/94 to be a grandfathered AW. If it left the factory as a lower receiver only, then you have the burden of proving that it was fully assembled before the cut-off date.
With the AW ban set to expire 9 months from today, I personally would try to hold out and see how it all pans out. You definitely don't want to pay big bucks for something you can buy for less than a grand in three quarters of a year. I'd recommend getting a post-ban rifle for now, and then if the ban sunsets and is not replaced, either convert your post-ban to a legal full-feature rifle or replace it with a factory-new one.