I think Smoker should be his rival.
-Its only fair for Smoker to get whipped this arc b/c he whipped Luffy in part 1.
--The purpose of Smoker losing shows how powerful the enemies in the New World are, and How much Luffy has to grow if he wants to be the best
As for Luffy's enemy that has to be the Magma guy um...Akainu
-For simple reasons everyone knows.
I feel like Cody will be there to stop Luffy, but in the end only help him