Out of Senju, only Hashirama and his inherited physical characteristics matter. Tsunade is a fodder, and Tobirama was defeated by some Genkau, whatever, Henkaku psedu-jins, with tools that surprisingly, the genius Tobirama could not beat.
Uchiha are potentially the strongest clan, but none of them aside Madara could reveal the secret behind their MS/EMS potential. And i doubt many will go ahead and just start killing their best friends, or be able to find extreme emotional stress. Something like that just does not lie around the floor.
Uzumaki were a clan that practicied very powerful fuinjutsu, and all had a great amount of chakra. If i am not mistaken, fuinjutsu demands even more intellect that genjutsu (oh poor Naruto lol...). They did not need some sort of vague power-up as MS-trade for emotional stress. And they were most feared and got destroyed.
Hands down, Uzumaki.