I think the best AR is the one that best meets your own subjective needs for quality, reliability, affordability, and perhaps collectability. The answer to the question is obviously going to vary considerably between individuals.
For me, the answer to that question is Colt. But it's not for me to fault someone else who finds that Bushmaster, ArmaLite, PWA, or whatever provides an equally appropriate answer for them. Heck, if you can get a cheap Hesse to run right I say more power to you.