who is stronger?
mei
tsunade
I'm going with Mei, she has a wider variety of jutsus that she can use and she can fight at any distances pretty much. I also can see her using a Lava shadow clone like how Kakashi used a lightning Shadow clone which would melt her enemies who try attacking her in taijutsu.
Tsunade moves way faster than Mei does her handseals, which was already proven in the manga.
Tsunade beats Mei.
You do know Tsunade was already in front of Mei so are you saying Mei is suppose to do her hand signs faster than Tsunade jumping forward when she was already closer towards Madara? Mei was taking hits from Susanoo's and unlike Tsunade, she can't heal her wounds so that's a bad example and doesn't really prove anything.
Mei can use Water, earth, fire, Lava (earth+Fire), acid/boiling (fire+water). Mei can attack from many different angles. Possible jutsus are hidden mist, lava shadow clone, various earth, fire, and water jutsus, boiling mist which can burn the inside of who breathes it in while also melting their outsides.