I can't believe this is being debated right now, Minato wins hands down, not saying it will be easy, but nonetheless he will still win. Are we forgetting that Oro has no way to touch Minato, even in Minato's base speed Oro would have a hard time trying to land a blow on him, there's just no way for him to do it.
And someone show me where it says Rasengan can't harm Oro?? Oro isn't even that strong, he's just hard to kill with a bunch of overrated forbidden jutsu, but I do give him credit because of those things. Please don't compare Naruto's Rasengan to his fathers' because Minato's is 2x bigger and more powerful then Narutos', He damaged Tobi with a Rasengan and made him retreat, need I remind you Tobi had the cells of the first Hokage in him, Senju DNA which is hella strong, give me a break, if he can do that to Tobi he sure as hell can do it to Oro.
I see it like this, Minato dances around Oro with a barrage Rasengan, Oro heals himself (limited to about a few heals) until he runs out of chakra. While Oro is weak and pathetic Minato comes in with a FTG head chop, Oro is done. U_U