First: College, for the team ethic and the fact that they're human - they make mistakes, they all try hard, they're not so far up themselves so that they have to find someone to blame for their mistakes and misses, and they haven't screwed around with the rules as much as the NBA.
Second: NBL, for similar reasons, but the variety of athleticism and skills isn't as good as college.
Third: NBA, for the high quality of offensive skills and athleticism, but I hate the way they've screwed around with the rules, and the emphasis on flashy iso plays and highlight reels.
Fourth: Euro ball, which is spoilt by the thuggery they allow, and is sooooo slow (and you just KNOW they're going to foul to stop any fast-breaks or inside shots).