It is obviously Tsunade
she can't survive lava release I don't care how well she can regenerate she still feels pain and feeling your flesh & skin melt is far to much for any human.
Tsunade can't touch Garra because of his sand he could simply crush her under a sand tsunami similer to what was done to Kimimaro.
people are saying Tsunade but she was the one that stood up to madara and broke his guard, who legs where shaking in fear against madara again and barely did nothing ? thats right mei terumi the weakest kage -_-