Insane Genis easily.
Without amps, I'd have to say Thor. His offensive output is pretty ridiculous.
Keeper Surfer is a completely different character. Thor has an outside power source... probably would have been easier to just use King Thor or Rune King Thor. Gladiator has an outside power source as well, and his power along with many others and the Uni Power was apparently less than Surfer's...
Strange might as well not have changed.
Added in King Thor and Rune King Thor. But the Runes are not Thor's power. So it is fair for Gladiator to have Uni Power and Surfer to have the Keeper Bands
Without amp, I say current Silver Surfer (when powered, of course!)
With amp, I really don't know. Keeper Surfer with training was able to keep up with Galactus, which put him way above any version of Thor and SS Strange, as well as Void/Sentry (which I still think that a regular Thor, Hulk or Surfer shouldn't have any problem with it, also, what a poor character!) and probably over Gladiator too. I don't know for Insane Genis.