I chose Goku, but it depends on the point in the series.
Goku at the beginning DBZ would get killed by Superman. Not that fast or with energy attacks that good.
After King Kai's initial training, Goku still wasn't quite there. Like, he was fast and had the Kai-Ken, but his energy had to run out at some point. Even if he fired the beam with enough energy to destroy Earth (like he did to counter Vegeta's galic-gun), Superman could easily just run around it and kill Goku with a well-placed punch to the Stomache.
But once Goku trained on the ship at 100x gravity, things started to shift. His speed had become just as Super-human as Superman's, and he was developing the strength and absurd energy attacks to match. I'd still say you could argue this though.
But once he got out of the rejuvenation tank, he was battling Freiza, an opponent stronger than Superman, semi-competitively. And once he goes Super Saiyan I don't see how it's a debate anymore.