If it's Strongest and not more Powerful obviously it's Tsunade,IMO we haven't seen Hashi bustin the ground with strength alone something Tsunade effortlessly do,I even doubt he'll be able to lift Gamabunta's sword without SM.
So the people saying Hashi please pay attention to the words Strongest in base,don't just answer lije donkeys
Base seems to vary depending on Character, so it's a completely pointless measurement. How is Sharingan not base, if Mokuton is? In that case, i would say that the strongest in Base is Kaguya, with her base being: Not having Byakugan on.