I counted all the votes and this is the current result:
Sans: 10 (Mariogoods, TheArsenal1212, BruceTheBatman, SansTheSkeleton101, Apatheticskell, TheBoneyBoi, HardCorenerd, Dragonboi9191, Calciumandbones (probably sockpuppet but he talked more than FRA), Luke Merod)
Undyne: 10~11 (ApiesDeathbyLazors, Ricsi-viragosi, Wokistan?, Deucalion.Nikos, Calaca Vs, Demon Takumo (his argument about Undyne's HP is wrong but the rest of his arguments are correct), Fastrthnwind, ThePixelKirby, Rodri Dante, ShakeResounding, FloweryAlex (not sure if it's sockpuppet but he gave more reasons than the others and kept discussing in the thread for a while)
Incon: 1 (Jimboydejuan12)
Votes not counted: Videogamer1265 (assumed things such as Sans being combat smarter and being capable of switch green to blue mode). KarmatheKing (badly smells to sockpuppet and even then he didn't gave good reasons), Waluigiisomnipotent (more sockpuppet smell),
So right now it's inconclusive and Undyne has the advantage.
EDIT: BTW Undyne was the first to reach the 7 votes. Funny fact.