User blog comment:TehAnonymous/TehAnonymous AMA/@comment-7145241-20150219235713/@comment-1990160-20150220052205

Oh, right, that's a spell.

This is a tough one - though I know of all champion abilities, I can't remember all 500+ of them with their names & details... additionally abilities in a vacuum are pretty weak - champion kit synergies amplify the power of individual abilities by a solid factor.

For raw power and utility... I'd have to go with.