He isn't the best ever...I'd say easy top 5. The thing with Brett is he never had near the weapons that many of the other hall of famer QB's have had. And he has always had an OK o-line. Brett was/is the best of making do with what he has...last season, he had 5 go to WR...most of them no one had heard of...so no he isn't the best ever...but he is one of the best ever.
Who's your best? Mine is Farve I never had a #1 I use to think John Elway Joe Montana Steve Young and Dan Marino were the best for me. Like you said Brett did the most with less.