Damage-wise: Attack Reels and Trigger Happy from FFX and X-2 slaughter Lion Heart. Even Blitz Ace does more damage if you have a good Tidus.

Best looking? I don't think so. I'm not particularly fond of the last few hits of Lion Heart. The whole spacey slash thing is just too over-the-top. And the final hit of the enemy unceremoniously hitting the ground is a rather drab finish.