i'm assuming classic CM. and i think this is a pretty good battle, actually. both can absorb crazy energy, but i think IM has more versatility. CM was one of those guys who was never really overpowered like so many of the current cosmics. he has some good feats but nothing like what some of the herald guys can do nowadays. i used to really like mar-vell, partly BECAUSE he was NOT unbeatable like ss and some of the other overpowered characters today.
current IM would win a slight majority imo.