Zoro vs Sanji would probably play out like this: First: Understand that Zoro is a swordsman .... he has the potential to One shot Sanji if he lands a clean attack. Logically Sanji cannot parry or counter Zoro's Bladed attacks with his kicks(atleast not for long)Zoro is proficient at armament haki but because sanji is profecient at observation haki, he would have an easy time not only dodging but landing attacks on Zoro.They would both have something to overcome, For Zoro: His biggest struggle would be landing an attack on Sanji, For Sanji: His struggle is damaging and knocking out Zoro. Sanjis speed and agility is what prevents the fight from being anything lower than mid diff, potentially high diff situation, cause Zoro might get fucked up quite a bit before he eventually lands a good attack on Sanji. Its just a matter of how long you think sanji can avoid attacks from zoro and how many attacks from sanji can zoro take. So most likely Zoro in a High diff fight. (potentially mid diff) most likely high diff tho.
post it in the zoro vs sanji battledome thread if you want to