Meta Knight hands down is the quickest attacker.

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I think it's between:

Meta Knight or Fox.

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1.Sonic(duh)
2.Fox
3.CF
4.Snake(if you count his mortarslide)
5.Sheik
6.MK
7.Diddy
8.ZSS
9.Yoshi

I kind of wrote this while i was thinking, its possible I could have missed some characters

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Well...if you're talking about running speed...then it would be Sonic. Attack speed would be Meta Knight, Game and Watch, and Diddy Kong. But if you think about it...any character can be fast as long as you implement Shield Rolling and Side stepping the right way. Speed almost means nothing in this game.