Writing up comic book characters has been a tricky issue for as long as superhero RPGs have been around. There are a few related problems: first, comic book writers change power levels as needed to tell a good story. Second, many heroes could reasonably have about three different writeups - one when they're in their own book, one when they're guest-starring in another book, and one when they're appearing as part of a team. This means that there are multiple "right" versions of any character, and that setting power levels to simulate the highest power level a hero has exhibited will not capture some of the hero's stories very well.
There's two approaches that I find work well for conversions: first approach is to pick a comic era that has the sort of feel you want in your game and ignore other interpretations of the characters. For example, if you're a big fan of Ultimate X-Men, convert those writeups, which are generally less powerful than the 30something team in the main continuity. Second approach would be to describe your world in M&M terms and make characters fit the system, since they don't have consistent power levels in the books anyway.
There's two approaches that I find work well for conversions: first approach is to pick a comic era that has the sort of feel you want in your game and ignore other interpretations of the characters. For example, if you're a big fan of Ultimate X-Men, convert those writeups, which are generally less powerful than the 30something team in the main continuity. Second approach would be to describe your world in M&M terms and make characters fit the system, since they don't have consistent power levels in the books anyway.