Well, it would be hyperstorm IMO. 
Hyperstorm possesses virtually infinite psionic power which he can draw endlessly from 
hyperspace, from which (in the 
Marvel Universe) the primordial energies creating the 
fundamental forces of the 
universe, 
strong nuclear force, 
electromagnetism, the 
weak nuclear force and 
gravity flow into our plane of reality. Controlling the four fundamental forces should theoretically allow him to restructure, create or destroy matter at will down to subatomic level, as well as creating electromagnetic fields and electrical currents, making matter 
radioactive, manipulating gravity, causing nuclear detonations, emit enormous energy blasts, use his psionic powers to increase his physical strength and generally accomplishing nearly anything he sets his mind to. He has also displayed 
telepathic abilities, both as Hyperstorm (
Fantastic Four Unlimited #12) and as his otherworld counterpart David Richards (
Exiles #59). For the latter, his powers has been described as an amalgam of the powers of 
Professor X, 
Magneto and the 
Phoenix Force. He can also teleport through hyperspace from one place in the universe to another, possibly at immeasurable distances. He has been seen to counter the 
Invisible Woman's forcefield with one of his own making, unsurprisingly since she draws her power from one of the higher planes of hyperspace, though highly limited compared to Hyperstorm's own hyperpowers. He is also 
telekinetic, considering the fact that both his parents, as well as his grandmother 
Jean Grey, had telekinetic powers. His power level has generally been compared to that of 
cosmic beings rather than that of other very powerful 
mutants such as 
Franklin Richards or 
Nate Grey. Hyperstorm may be the most powerful mutant witnessed to date.