Voted Mihawk, Nasujuro and Shiryu.
Although I think it‘s feasible that Zoro vs Shiryu doesn’t actually happen (or Shiryu is basically fodderised by Zoro or Mihawk.
It depends when Cross Guild actually make their move. If it’s Strawhats vs Blackbeards vs Cross Guild at some point I could see Shiryu getting taken out as a sacrifical lamb so that Luffy vs Blackbeard and Zoro vs Mihawk can happen at the same time.
There’s a reasonable chance of a Beckman clash, although again, if Oda decides to include Cross Guild into Strawhats vs Red Hairs (as is also very possible, considering Buggy and Mihawk are both connected to Shanks) then it could be Zoro vs Mihawk at the same time as Luffy vs Shanks.
I don’t see Strawhats vs Marines happening, so I don’t see Zoro fighting any Admirals.
S Hawk, eh, could still be something that happens again before Egghead ends but I don’t think so.
And Nasujuro just seems likely to happen at some point.
SHs vs Marines (and thus Zoro vs Fuji) happens at Elbaf imo.
The SHs will be blamed for Vegapunk’s death, and Kizaru will likely die at the end of Egghead by sacrificing himself to let Bonney and the SHs escape. Akainu, who is already nearing his breaking point, will seek revenge against the SHs and Giants for the embarrassing Marine loss at Egghead, so he’ll lead a full-on Marine assault of Egghead.
Elbaf should already be on friendly terms with the SHs, so it’s hard to see there being a relevant group of enemy giants for the SHs to fight there. Even bringing back Meme for Elbaf would lack any tension since she already lost at Wano, and only a fragment of her crew would even be there (Smoothie and the others on the ship).
Taking on the Marines would be a good step up for the SHs (and they’d obviously have help from the giants to deal with the fodder army of Marines, and the Grand Fleet could show up too since at least Harjudin should be in Elbaf). Akainu will be a parallel to Surtur, the magma giant who started Ragnarok