Orochimaru, no debate. Why?
1. Nothing in Minato's arsenal of jutsu can KILL orochimaru.
2. Orochimaru was hiruzen's first choice pick for hokage...THEN jiraiya. THEN minato. That being said, this was Orochimaru back before he joined akatsuki and before he showcased his forbidden techniques. And yet, Hiruzen was positive he would be the best choice for hokage even though he knew of Minato's FTG. So put 2 and 2 together, Hiruzen indirectly says oro > minato.
3. Snakes always beat the toad...manda > gamabunta
4. Orochimaru's sealing jutsu can/will halt minato's flow of chakra, including the 9tails he still has inside of him. (i think he still has it anyway)
5. Leech all creation would make it impossible for Minato to land a critical blow with what little effective jutsu he has against oro. Throw in the Rebirth technique, and there's no way Orochimaru is dying.
That's only a few reasons.