My favorite superhero system is definitely Mutants & Masterminds. It's d20 and originally based on DnD, but both games have gone through a few new editions since then and they don't resemble each other as much any more.
It's
not class-based but uses point-buy character creation. It's not hard once you get the hang of it, but I'd definitely say there's more complexity in character creation than during play.
As for how well it'll work to emulate the series you mentioned... I can't say, as I'm not familiar with them. Sorry! But it is pretty versatile.
There's also the official DC comics game DC Adventures, which is actually the same system. The two games' rulebooks, the Hero's Handbooks, are almost identical except for the art and character names used in the example text, although the DC version does include some setting information and stats for some of the major NPCs (Superman, Wonder Woman, Lex Luthor, etc.).
There is an online SRD site available for the 3rd edition rules
here.