But what if in the beginning of the fight, the Raikage jus teleports to him and kicks his ass sooo hard that his sword goes flying somewhere jus like what 6th gate Guy did to Kisame. Or the Raikage can just Lariat and samehada may not even be fast enuf to react u know swing so the Raikage knocks his head off. But even if we say Kisame fused with Samehada then still the Raikage cud just get out of the water dome or use his crazy teleportation skills then kick his ass with taijutsu on land or maybe kisame wont even have enuf time to get water dome, as soon as he merges he gets his ass kicked by taijutsu. There is like nothing Kisame can do about a giant black man beating the shit out of him. I go with Raikage with the hardest difficulty.Kisame with only slightly high difficulty. A has no counter to water prison and the water dome and stuff like that. Once he is in that it is over for him. And his lariat wouldn't work because Samehada absorbs chakra as it comes near. Remember Bee's raiton enhanced swords that he threw?
Samehada just makes people OP, especially if they are able to fuse with it and use it like Kisame does in the water dome.