IMO this would be a very close battle. Lets break it down.
Tsunade:
Pros: Massive Strength, agil, best medical ninjutsu in the series, highly versatile in poisons and several defensive ninjutsu. Close range fighter
Cons: So far Lacks Offensive jutsu, heavily relies on tie jutsu, more effective as a support, when on offensive mostly will be as a melee shinobi. Weak if separate the distance from her fists.
Mizukage Mei Terumi:
Pros: Has 2 Kekki Genkai, analytical notices the battlefield i.e when she fought sasuke and noticed the hole in the wall and utilized it to corner sasuke with her Lava Kekki, Range fighter
Cons: So far havn't seen to possess a high strength in tai jutsu as seen when she hasn't made the decision to fight Hand to Hand with Sasuke, Weak if you close the distance.
My decision as for a 1v1 i believe Misukage has the upper hand with her more dynamic offensive jutsu. However i will respect Tsunades agil, str, and healing capabilities, but those can be impaired with Mizukage's AoE (Area of Effect) kekki GenKai Boil Release ninjutsu and Lava Release ninjutsu to create obstacles for Tsunade's CQC (Close Quarters Combat).
That it is my explanation on who but please elaborate more onto it preferably against mine so as i may know more of Tsunade's adaptability to this situation.
