i think mifune is better, as he is a samurai and he have more experience and also he is the leader of all samurai and have been surviving in the ninja world with pure kenjutsu.
Mifune is better but sasuke would win. So far mifune is only seen useing one sword so it would be alot easier for sasuke to predict his sword movements with his sharigan. Bee used seven swords and an unknown style where the swords always spining which make it extremely difficult to keep up with.