I'm going to have to go with Buutenks on this one. While Super Janemba did give SSJ3 Goku and SSJ2 Vegeta a run for their money. As soon as Super Saiyan Gogeta appeared he was absolutely smoked. I think it would be a little close because Buutenks is definitely not Buuhan, but Buu's regenerative powers would wear on Janemba. Even if Janemba would remain mobile through his phase teleportation.