It depends on which edition you're looking at. I've played both the original Pulp City and SuperSystem 3rd edition. There are new editions out for both: Pulp City Supreme Ed, and SuperSystem 4th Ed. I own and have read through the new PC rule book, but haven't looked at SS 4th. Styx and a few others on the boards might be able to speak to them in more detail.
It also depends on what kind of gaming you want to do. If you want pre-made heroes you really only have two options: Pulp City or Batman Miniatures Game. Both are great games, but neither has the tools to create characters.
SuperSystem and Power Legion (from Ganesha Games) both have creation toolkits for making your own characters. I've got Power Legion and it's pretty good, but lacking a bit of support from the designer at the moment. He's a one-man shop so he gets distracted pretty easily after releasing a rules set. If you try out Power Legion, err on the side of less is more, especially when it comes to giving characters the Armour special rule.