Prof. X? A great character that's been kinda ruined these last twenty years. Sorry but there's been too much terrible stuff that writers have done with him.
Moonstone has become one of the most interesting to read villains in Marvel, though I think what's holding her back from A list status is she has no real goals lor strong motivations. She's not a rule the world type, though she'll go along on the ride in a hench capacity for those that do. She doesn't have a real figure to concentrate on for revenge or the like. She doesn't have deep convictions , really, she's a survivor with a bit of a superiority complex. I think of her in a way, like Johns' ROGUES. A pro villain that doesn't have timr for the usual nonsense of ruling the world or wiping out a country. God forbid she ever does get a serious motivation though. She'd be a hell of a threat on multiple levels to any team or solo hero.