Venus at Final War. Thematically and narratively he makes the most sense.
Mihawk/Shiryuu (i don't think a legit Dracule vs Zoro is happening in the first place) -> Venus -> clash with Tashigi/off-panel fight in some epilogue
Venus, if his Haki on par with Topman's has better Haki than the other two. He has DF powers. Most importantly, he has centuries upon centuries of swordsmanship history for Oda to expand into in his fight with Zoro. This man of course also has had centuries upon centuries to develop his swordsmanship. There's also the theme of Heaven tied with Zoro's ultimate goal and Venus being a Warrior God.
Zoro will already be superior to Dracule when entering the Final war.