It's really hard to say. The Joker is extremely cunning and has a lot of tricks up his sleeve. But Sweet Tooth is very strong and not afraid to use brute force. If it's a fight in a confined space, Sweet Tooth might have the upper hand with his physical strength. But if it's a more strategic battle, the Joker could outwit him.
In the 'Joker vs Sweet Tooth reaction fanfiction', there's no clear - cut winner. The Joker is a master of mind games and has a lot of resources at his disposal in Gotham. But Sweet Tooth is a force of nature in his own world. If they were to meet, the Joker might try to use his charm and wits to get Sweet Tooth on his side, but Sweet Tooth's loyalty to his own cause could make that difficult. And if it comes down to a physical confrontation, Sweet Tooth's physical prowess could be a major factor, but the Joker could always have a hidden weapon or a backup plan. So, it really depends on how the author wants to write the story.