Re: Who was the best water release (suiton) user?
The problem with comparing these two ninja in terms of water techniques, is that Tobirama has only been presented to us in Part I.
I'm sure we've all noticed that Kishimoto has begun to walk the path of DBZ, and this manga has become flashy, with overdone and overpowered jutsu; so its no wonder Kisame in Part II would outdo Tobirama in Part I.
When we saw Edo-Hashirama fight, no one even gave that dude a second thought right?
Now Hashirama is thought of as the godliest shinobi to ever live by many of NB. You just can't compare power levels in Part I to power levels in Part II.
That being said, if Kishimoto would be inclined to give Tobirama some screen time in Part II (Like he how he is showing us Hashirama through Edo-Madara) then I'm sure Tobirama would easily outclass Kisame when it comes to suiton; because that is literally what he was known for. He wasn't considered the best for nothing.
By actual manga feats, Kisame takes it. By hype and my personal opinion, Tobirama takes it.