I think it'll be either of these
Sasuke - If Kishi he wants this "Hokage" this to come off as serious, he needs to do something huge. Naruto did the final blow to Obito via TnJ so Sasuke will do the final blow or will lead the assault or w/e. I have a scenario in my head where the Hashi prediction of Sasuke changing Madara through words because of "Izuna" comes true - except Sasuke uses this to his advantage and coldly kills him when his guard is down.
A simple combination attack
Obito - This would be the the best of the three from a story-standpoint. Though, he's probably dead.