KingDubya
Mainstream Indie Rocker
It all depends upon how powerful Goku is at this moment. If you are talking about somewhere from Dragonball to the start of the Saiyan Saga in DBZ, Zero has a chance of winning since Goku is the farthest from his full potential at this point. Near the end of the Saiyan Saga, Goku has the better chance, but Zero could still win. During or after the Frieza Saga, Goku would kick *** with his Kaio-Ken technique or goin SS. If he went SS4 (would have to take place after or at the end of DBGT), he'd destroy Zero within .3 seconds after the transformation. And if he did a fusion with Vegeta (therefore creating Vegito), Zero wouldn't know what hit him.
PS - I am not a fan of Dragonball, DBZ, or DBGT, even though I do know a lot about it.