I really don't think it's fair that everyone is underrating Mei.
First of all the latest chapter she is shown using a water wall type of technique which was able to extinguish madaras enormous fire technique and she was able to go into the water dragon bullet technique with NO handseals and she used the same water she used for the water wall. Plus there's the fact we don't know much about her yet, same thing with Tobirama. Mei can also use 5 different elements(water, earth, fire, boil, lava) and has been shown to be pretty intelligent(trapping sasuke, realizing Ao was under Fu's control).
On Tobirama's side he has incredible chakra, supposedly best water user(not sure if this is just in the leaf village or what), sword of lightning, and as well as a genjutsu user. But people keep saying he also had the edo tensei, but the fact that he never mastered the edo tensei might backfire for him plus its a forbidden technique and i doubt he would want to disturb the dead(being a respectful person it seems like). And we don't know if Mei has any sealing techniques, she is a kage you never know.
As far as the series is right now i would say Tobirama would win(being a Mei fan myself) but I feel like she has many more tricks up her sleeve then what Kishi has shown us so far. For water techniques i'd say she is on par, if not surpassed him with water techniques only.
And can someone show me when they learned in what chapter/episode that he had teleportation as well, I think I missed it(havn't really watched any episodes lately

)