again tsunade wins, her superior medical + taijutsu is phenomenal, again she was 2nd pick for hokage, only coming up short to j-man, that in itself is a incredible feat to her prowess as a kunoichi of konoha.
gai may have his gates, but none of them have the power to take tsunade, unless he uses the 8th gate, if so he will most definitely win...at the cost of his own life.
gai is faster then tsunade thats no surprise, but IMO counters with intelligence which is far greater than gai's, both of there taijutsu's are at master lvls, gai and his gates right up to seven has increased his strength in his taijutsu to the point he can take on reasonably strong shinobis and beating them with little effort but risk damaging his body, tsunade already has raw strength, given her superior chakra control skills, she developed her chakra enhanced strength know as her incredible raw strength, gai has ninjutsu and genjutsu skills, but tsunade's is far superior.
tsunade's close-range combat skills have been considered unsurpassed. Jiraiya commented that no one could stand equal to her in terms of combat and medical prowess.
so again im going to say tsunade