Naruto vs. Killer B
I have no personal favorite but when u actually think about it this would be a very close battle.
Naruto:he has the stronger Bijuu, he can combine his bijuu with sage mode, he is at an elemental advantage since he is a wind user.
Killer Bee: He has the most experience with his bijuu and has mastered one of the strongest attacks in the show the tailed beast bomb (kisi kinda hinted that it is stronger then the rasenshuriken) and he has Samehada.
I think this would be a close battle personally, i think Samehada will give Killer Bee more of an advantage over Naruto cause of narutos fighting style, but im sure that all the naruto fans on sayan island will find a way to defend their favorite characters.
Side-question: If u think Killer Bee is stronger then should he be a better fit to fight sasuke? (although it doesn't matter cuz the final fight will be naruto vs. sasuke)