Why are people sleeping on Hotei, The mirawarigumi leader? He's a samurai and should be a high tier one.
For me personally I'd like it if Zoro faces a swordsman in a pure swordsmanship fight.
King, Queen and Smoothie would great fights for Zoro, but I'd take a pure swordsman over them to face Zoro any time of the day.
Now the only pure swordsman left who might be a challenge for Zoro is Hotei. Eventhough it's a long shot I'm hoping he's a hight tier swordsman that can push Zoro to 100%.