1.Tsunade (But only if she can land a hit, otherwise Gai's speed would be too much for her.)
2. Minato with FTG for sure, without FTG am not sure, his base speed was implied to be equal to A in version 1 by C (Raikage's genjutsu body guard) though.
3. Third and Fourth Raikage no doubt at all. Afternoon tiger couldnt even kill Kisame, it wont even faze any of these two with raiton armour on, even without armour it would only inflict minor damage considering that they are way moore durable then Kisame. Afternoon tiger may not even hit, A dodged Jugo's chakra blast from point blank range in v1, he'll dodge afternoon tiger.
4. Kimimaro...Guy's base taijutsu is useless against shikotsumyako, bone armour will protect him from 7 gates morning pickock and afternoon tiger. Gai could win if Kimimaro is sick like he was against Gaara and lee, but if healthy, he stands no chance.
5) Naruto in sage mode, pretty sure that even in base, Naruto would be able to withstand afternoon tiger, lets not forget that he withstood a shinra tensei that was able to pawn THREE BOSS LEVEL SUMMONS (Uzumaki durability). if he in sage mode, then he will be almost if not as fast as Gai and frog Kata will do the business. KM Naruto would also pawn guy, too fast for even uy's gates and he got extra chakra limbs, Gai has no chance.
6) Jugo could possibly do it, even in his VERY weakened state (Kid mode after healing Sasuke against Bee), he was able to keep up with V1 Raikage in terms of speed/reflex/reaction time and he got insane Durabilty. He also got super strength and speed when he uses his jet boosters to increase the power of his attacks and to propel himself at great speeds (similar to asura path), can turn any part into a weapon and can project a needle that absorbs people into himself, dangerous if gai gets close. Can counter afternoon tiger with chakra cannons too and has more then enough chakra to outlast gai in stamina.
There are others but I will stop there, not all of them are givens anyway, some of them could go either way depending on plot, but the A and his Dad are certainties, Naruto and Minato (with FTG) are also a certainty.