I'd prefer Mihawk being his last opponent but I think his last opponent may nor be any of them, but rather that guy from the Gorosei with the katana.
I have been thinking about Mihawk. About how can Mihawk appear as a big boss for Zoro that doesn't feel out of place to the story. The guy lives alone in an island, with no allies and no crew and apparently no interest in the One Piece or in piracy in general. Zoro vs Mihawk can happen at any time if Oda chooses it, but it needs to feel like it's part of the bigger plot so he can explore more of Mihawk's story and origins in a way that feels natural and part of the bigger plot, and not just a random miniarc of "Hey, I'll go challenge Mihawk now, you guys wait here".
I don't know how it will happen, but here's a crazy possibility: Mihawk may ber related to Im and if Luffy eventually fights Im for real, Mihawk would get his past revealed (something similar to Doflamingo's past, perhaps) and serve as a boss to Zoro that has at least some ties to the actual story of the series. In this way, Zoro would also reach his dream in his last fight.
It's a longshot but I don't think their eyes are a coincidence so I think there will be some link, even if superficial.
The other possibility is that Mihawk goes down before they reach Laugh Tale so that Luffy can achieve his dream before Luffy but I don't think the order is that important, since Laugh Tale is only the beginning of Luffy's legacy eitherway.
I just want Mihawk's arc and downfall, whenever it arrives, to feel satisfactory.