Re: Champions vs other systems
I own and have read all the systems you named, but the only one I have played (besides Hero) is Silver Age Sentinels. My opinions on the others should be taken as being less informed.
Aberrant: The background is too dark for me (as befits the source, I suppose). And I have never liked the Storyteller mechanics. This is probably my least favourite.
Mutants & Masterminds: I really like the background presented in the Freedom City supplement, and the game is pretty well supported by Green Ronin and it's fan community. However, due to some deficiency on my part (despite two readings of the rules), I just can't make sense of the mechanics.
Silver Age Sentinels: Easily my favourite in this list. Character creation is simple enough. I view the three stats as more of a feature than a limitation. Powers are reasonably straight-forward for those coming from Hero to understand. Fans on the GoO board are generally friendly and helpful, though the traffic there is lighter than here. Company support (in the form of new material) is spotty, which is kind of a turn-off. The Empire City background is, IMO, the best of any published shrpg. The Reality Storm supplement (with it's official conversion system for Hero/SAS) makes material from one system transportable to the other w/o much trouble. I agree with Oddhat's assessment that it is not as easily tweakable as Hero.
Godlike: I've toyed with this system (haven't actually gamed with it). I like the semi-realistic "WWII with supers" background, although the hoops the writers jump through to ensure that the outcome does not deviate far from the historical is a bit annoying. I find the mechanics a bit clunky, though they seem playable.
Marvel Universe: On the positive side: It's Marvel. Write-ups are available for pretty much all the major characters in the Marvel Universe. OTOH, the mechanics are quirky to the point of obscurity. I'd say they are the weakest of these games.