Kefka wins because he's mean and evil enough to open the battle by casting Stop.
Is Goku wearing a Ribbon? Great!
...Except that Ribbons don't protect from Time Magic.
This is the only imaginable scenario in which Kefka comes out the victor without Goku receiving outside help. Otherwise, Goku is waaaay out of Kefka's league.
@ Sephiroth: Sorry there, old chap. I'm a comm major too...I just focus on 5 minute songs.
ninja edit
If Goku brings a peace ring and Hermes sandals to the battle Kefka's screwed harder than an IKEA TV shelf