Up here at number 10 because he's not that complex, The Flash's impressive moveset is still one of the most varied across the whole game.
Comprising a low three-hit combo, various four-hit launchers and various specials that'll lock an opponent into being hit repeatedly for a few seconds, all of this takes on another dimension of effectiveness with his signature slow-motion toggle. Hit circle/B and the fight will slow to a crawl, letting you keep any foe airborne far easier and longer by wailing on the aforementioned combos.
Once you get the feel for how all of Flash's moves can be linked together, take note of catching your opponent in Fists of Fury (it'll pull them out of any falling animation) and you can keep up the punishment, finishing them off with the unlockable Sonic Bolt projectile from across the screen.
They won't know what hit them.