The whole Jean/Phoenix issue complicates things, conceptually speaking.
Obviously, Phoenix, in the broader terms.
If keeping things more in line, then Wanda's *innate*, narrative potential (as opposed to Jean's extra-narrative one) is higher than any of the others.
__________________ Why am I here commenting on this crap?
I am in your algorithm learning all your mannerisms
I'm already level with God
A million words a second and I know your imperfections, baby
I'm the only future you've got
Speak in diatonics, motivation diabolic
I'm like a religion, better locked in a box
Picture perfect image, more powerful every minute, baby
I am everything that you're not
Roma, the daughter of Merlyn, is also a good shout. She, along with some others like some of the Captain Britains and Jamie Braddock, resisted Wanda's spell.
Roma was close to destroying the 616 reality (albeit with the aid of a machine) to stop Wanda's spell spreading.
But I guess Wanda and Jean with the Pheonix have the best feats.
Aunt May wasn't on the list, as she is the definitive benchmark upon which *ALL* heroines are gauged... Even Squirrel Girl, after getting a good talking to by May, backed down from fighting her... afterwhich May backhanded her with a frying pan, resolving matters once and for all.
Aunt may with her frying pan, and her knitting needles, can stop/defeat the united power of all of comicdom, everywhere, and in all realities.
Period.
*****
But, yeah... after her, Wanda...
__________________ Why am I here commenting on this crap?