While I would normally vote for Gohan here. Superboy Prime is an angry douchebag who is willing to kill anything in his way. Gohan has more reserves and would most likely hold back even in a complete blood lust (hell he got beaten by buu). It would probably be Gohan on defense the entire match, however Superboy could easily end it by taking Gohan out of the atmosphere. Superboy can breathe in space, Gohan can't.