Orochimaru takes this, in my opinion. While Pain may have an advantage in AP it's not like it means much since it goes to waste against Orochimaru's body type. That guy is basically un-killable in Naruto because of his snake like body that absorbs physical brute force like (quoting SpongeBob - "like some sort of spongey material"). So things like the Almighty Push while it will knock him around and most likely break some things, like a second later he's back up on his feet and ready to exploit that 5 second weakness. The closest thing Pain can try to "kill" Orochimaru is explosive (and hopes they incinerate his entire body, or Soul Stealing, of which means he's got to get in Orochimaru's personal space to achieve which will make easy way for Sasuke's sharingan genjutsu.) The planetary devastation can be used to "seal" him in a sense but just like Naruto he could dig his way out.
As for the versitality, I'm sorry but... HA!!! Orochimaru has basically almost everything Pain has and more. He can match chakra absorption with chakra absorption, giant summoning with giant summoning (and like manda's his snakes are versatile enough to fight two giant monsters (the toad and slug), he can reanimate the dead, activate genjutsu (something Pain has no counter for), he can attack with an endless amount of snakes, he can activate the Giant White Snake mode to both possess and eliminate a Pain body or allow it to become damaged so it's vaporized blood will paralyze, the list goes on.
And on top of that Orochimaru is a genius both jutsu wise and tactical wise, with prep time and knowledge you just allow him to exploit every single weakness Pain has, and there's a few biggies. So Orochimaru can simply attack from a close range, mid range, and long range at the same time, and toy with Pain who for the first time in his life will be the one overwhelmed by numbers and an enemy he doesn't fully understand.
Orochimaru, high difficulty but I'd say a good 7-8 times out of 10.
