Jean Grey is the most powerful mutant. This is canon, incidentally. She has been specifically referred to as "the ultimate mutation." The Phoenix Force, which is Jean's by right of blood, has been specifically referred to as second only to the creator, and we have seen her perform feats of just that level. This is canon supported by at least four different writers at this point -- maybe more -- and I'm willing to bet that a reasonable amount of people here can even point to the exact place in the comics where this was stated. It is not wild, unspeculated fanboy musing.
And for the love of Buddha, Jamie Braddock is not an omega class mutant. I don't even understand why you would think that, it's not as if we haven't had dozens upon dozens of discussions on this very subject on this very board which I'm willing to bet that you yourself participated in.
See, this is the only thing wrong with having omega class mutants. For some reason, no one can figure out or remember what being an omega class mutant actually means, despite the fact that it is constantly spelled out for them. Being an omega class mutant does not necessarily mean that you can "kick the living crap" out of someone. So whether or not Franklin could kick Iceman's ass has no bearing at all, whatsoever, or whether either of them are omega class or not. Colossus could kill Elixir with his pinky, but Josh is an omega class mutant whereas Colossus isn't. Emma Frost did beat Rachel Grey in a telepathic battle, but Rachel is omega and Emma is bush-league. That is simply not what the category is about, and the fact that it constantly gets brought up, even in jest or derision, just shows that people are still missing the point.
Being an omega class mutant means you have unlimited potential. And yes, it's exactly what it sounds like. Not "unlimited destruction," not "unlimited strength," and not "unlimited killing." Unlimited potential. Why is there even any confusion? I just don't understand it. It means exactly what it sounds like. Seriously, everyone in this entire forum should just go and read X-Men Forever already. I'm not even kidding, that alone would solve pretty much all the problems. That one single miniseries answers every single question you could possibly have about omega class mutants.