Kidd and Law are captains who are fighting a yonko, so they will most likely receive the bigger bounty. That's only if they actually defeat Big Mom.
If Luffy defeats Kaido single-handedly then he will leave with the highest bounty. Although a lot of characters have been fighting Kaido, we know Luffy will get all of the credit.
Zoro will probably get the highest bounty increase but it will be less than Law and Kidd. If Zoro defeats King, then wouldn't his bounty surpass a billion berries?