Until we see Tobirama fight more and learn some of his skills, we really can't debate. Although I think he could be a major butt kicker with his space/time ninjutsu and decent edo tensei. I heard he is a good genjutsu user also. IMO he could be in the top 3 water users in the manga. He could also be pretty could with that Sword of the Thunder God. But I am very biast so I could be wrong. Tobirama could have absolute crap in S/T jutsu, and his edo tensei could suck completely. His skill with that sword could be incorrect also.