Kurotsuchi, because he's smarter than Caesar and Caesar kind of sucked as a scientist. I assume that Kurotsuchi's Bankai poison probably wouldn't affect Caesar much, however, we know fully well that Kurotsuchi has a back-up plan for anything and everything.

except kurotsuchi's reishi devices wouldn't effect him and he's a logia type

I can't see Caesar winning this. Mayuri is incredibly malleable when it comes to dealing with poisons, making it extremely difficult for Caesar to do him any major damage. He's likely physically stronger, and given his flash step, faster as well. But really, his physical strength hardly matters due to the Logia aspect. So why would he win this? Drugs! Even if we assume his reishi devices don't work, Logia users are still very much vulnerable to all manner of drugs, and Mayuri is full of them, not to mention they have a broad variety of ways to use them. I can't see Caesar winning because Mayuri can adapt to him, whereas Caesar has no chance of adapting to Mayuri.