Well, I'm not really into the superhero genre. The early comics I read were very poor quality and I just can't get into the idea of people jumping around in leotards shooting laser beams out of their noses.
But I have played GURPS Supers, Mutants & Masterminds, and Basic Action Super Heroes and I've run Teenage Mutant Ninja Turtles & Other Strangeness. The concept of TNMT was the most fun, but the rules for BASH are very fast playing and enjoyable. The others had too much fiddly point-buy accounting exercises and unexciting rules at the table. Overall I'd go with Teenage Mutant Ninja Turtles & Other Strangeness as the most fun, despite the clunky Palladium rules.