Ah, but Twilight isn't just a magic user, is she? It's her big thing, second only to reading. Not just some special ability; her passion. Would you make Twilight Sparkle the pampered, book-reading snob and Applejack the wizard who lives in the woods and solves mysteris of the universe?
There is Mabaa, who is one of the most powerful witches, able to make barriers, teleport, and a bunch of other fun stuff. Then there's Kim, who is admittedly restricted mostly to healing. Like I said before, Eureka Frog might also work, if only because destructive magical numbers? I dunno.
Eh, I suppose people just don't typically share my logic. I like to balance between skill and personality, and this will be harder as I am not as up-to-date as some on Soul Eater.
That said? Gonna be honest. I just really don't care for Death the Kid. Not sure why, always found him annoying. More "Rarity" than Twilight. Might just be my opinion though.