Zoro and that's pretty certain considering Oda has implied that on numerous occasions on several ways. It would definitely not be an easy fight, but that Zoro is still a lvl above Sanji is quite certain.
1) Zoro has always beaten the person who was confirmed to be the 2nd strongest of the opposing enemies: Daz Bones, the sunglasses guy on Skypea, Kaku, Hyouzou...
2) Zoro was the first person after Luffy who got a bounty and even after Sanji got a bounty too, Zoro's has always been higher. Zoro was part of the Eleven Supernova's, Sanji wasn't.
3) People are afraid of Zoro, he's considered by most people as the most dangerous member of the crew outside Luffy and is Luffy's first mate. They have said on multiple occasions that he could be a captain on his own. None of those things apply to Sanji.
4) One of the most symbolical scenes out of OP is when Zoro knocks out Sanji and takes all the damage Luffy took after Moria's fight. Due to that situation you can't say that Zoro "beat" Sanji that way, however the symbolical meaning behind it is clear: Zoro is the number 2 of the group, not Sanji.
5) The only person who has shown a greater resolve than Zoro is Luffy.
Zoro is stronger and that's not something you can deny as Oda has stated that frequently. It would be far from an easy fight, but in the end he's going to have the edge on Sanji.
Well... I would say Zoro with difficulty.
My reasoning is because Sanji is much stronger than given credit for when being compared with Zoro and Luffy. Also, most are probably saying Zoro because of his swords and being able to cut Sanji but people are acting like Sanji can't fight a sword user? Theres been plenty of seens in the anime (Just an example, don't give me thats not manga crap) where u see Sanji fighting with Zoro even when he is using his swords and u notice Sanji always kicking them away.
IMO If Sanji could get a clean Diable Jinbe (spelling) on Zoro, it could possibly finish him. Plus how can Zoro even catch Sanji? Sanji not only can use Sky walk to take him to the skys but he is the fastest straw hat excluding Luffy's gear 2nd so I doubt those Air slashes can catch him. Not to mention setting his body on fire which could also hurt Zoro.
Im not saying Sanji can beat Zoro but I don't know where u guys are getting this "Easily" stuff from =/
There have never been such serious scenes. Nami just blasted Zoro, Luffy and Sanji miles away, how's that possible? And when a swordsman is on the same lvl or higher than a martial artist, he has the advantage. That's just shear logic. If the martial artist is stronger than the weapons don't really matter.
About the bolded part it's utterly useless to say such things. If Zoro can get one slash on Sanji, it could possibly finish him too. Such comments are completely worthless as if you get seastone cuffs on an admiral, even Buggy could potentially kill him. And Sanji probably has the edge when it comes to running speed, however that's something completely different than having the speed to execute your attacks. Usain Bolt is the fastest man in the world, do you think he's going to kick or hit faster than a martial artist? There is nothing that indicates Zoro is slower in the execution. On top of that Zoro is ridiculous fast too, he was able to dodge a bullet at nearly point-blank range and close the gap with the shooter in an instant. You also forget that Zoro already has beaten once an opponent who could use the Sky Walk skill and that Sanji can dodge and walk as much as he wants in the sky, it is not going to give him any victory. Unlike Sanji, Zoro has several long range attacks and some of them are very large scaled. If Sanji wants to beat Zoro, he will have to come close and the closer he gets, the higher the chances are he gets hit.
Zoro has been on fire before and to set him on fire he first needs to pass his swords.
I tried to convince you with arguments but now I know i was talking to an obsessed fanboy i'll stop after proving you wrong OR making you fail (because you like to say that) one more time.
Sanji has the most "tricks" of the whole mugiwara crew, but instead of a trick maybe you should see it as an attack. Tricks are stuff clowns do, you should know that.
Take a look here:
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Don't give me the bullshit:
I can prove that Sanji has fishman speed, you can't prove that Zoro is just as fast/faster. So instead of ignoring it by calling it bullshit, Sanji's speed is his weapon.
Sanji showed to be a great tactician when it comes to battle. So when he is evading attacks using skywalk he can think of a way to surprise the enemy with a diable jambe to the face with fishman speed.
So you and all the other people who think that Zoro will have an easy fight "fail"
Remember Usopp vs Luffy ?, don't underestimate a Mugiwara
He might have the most attacks, though they are the less diverse than most of the other strawhat members.
Zoro cut Hodi Jones in the water, they even said that how it could be possible that a human was faster than a fishman in water. So that Zoro's speed exceed that of a fishman has been pretty much proven, but Sanji is probably faster than a fishman too. And as I said there's a difference between running speed and the speed of your movements. Sanji can't really block Zoro's attacks, he has to evade, while Zoro can block Sanji's attacks.