This poll is probably more about who likes what sport/league than anything. People are going to choose whoever the commissioner is for their favorite league, because everyone always hates them. I do think that Bettman is definitely up there, despite not really giving a shit about the other leagues, if only because the NHL is the smallest and least profitable of all those leagues, has the most troubled teams and has had by far the worst record of work stoppages. I'm not so sure that a commish can have a huge impact on the quality of the on-field/ice action as a lot of that is dictated by the owners of the teams setting the rules. But the one area where the commish has near complete control is labor relations, and Bettman has proven to be an abject failure at it.
Selig I think should be a close runner up if only because MLB desperately needs a salary cap and a greater amount of parity between have and have not teams, and all the huge steroid problems it's had that the league turned a blind eye to for decades.
What about the NBA is so rigged or predetermined, by the way? And how is Stern responsible for that?