1 is for Luffy, I guess.
So for the other spot my bet is on Buggy, why not
Kid or Law can't be I think, because both contributed for BM's defeat in a similar degree (Kid more), but Oda doesnt like Kid too much and giving Law the title while throwing out Kid wouldnt make sense (or maybe Kid will be another one, who knows). And both don't have much influence in NW anyway. Kurohige needed to conquer WB's territories and defeat Marco and the remnants of this crew for it.
From Warlords side, Mihawk, Boa and Weevil makes no sense. Loners or very small influence.
Buggy said he will be a Yonko and before no one thought about him becoming a Shichibukai. He has influence and ppl think he is strong, probably like Shanks even, and he is a walking gag.