@Zeefer:
There are a couple of reasons that lead me to believe that Zoro is at least the second strongest.
And I shall go over all your points!
@Zeefer:
Zoro's dream is to become the strongest swordsman in the world, a goal second only to the goal of becoming the Pirate King in terms of difficulty. Therefore, it would not be unreasonable to assume that Zoro would have to be at least the second strongest of the Straw Hats to achieve his dream.
Actually, it is unreasonable. Having your goal being strong isn't the only reason to have strength. Just because his goal is to find All BLue doesn't mean Sanji doesn't care about strength; he needs strength to help protect Nami and Robin and the rest of the crew, he needs strength to help achieve his goal. He was trained under a very good fighter and that can't be taken lightly. Just because Zoro is aiming for a lofty goal doesn't mean he has to be stronger than somebody else.
@Zeefer:
During the Alabasta arc, Zoro fought Mr. 1 whereas Sanji fought Mr. 2. Presumably, the higher your number designation in the Baroque works organization, the stronger you have to be. Therefore, by implication at least, Zoro is stronger than Sanji.
Also note that while Mr. 1 might be stronger, we don't know how much stronger. And Zoro's defeat of Mr. 1 was a LOT closer than Sanji's fight against Mr. 2. So those fights really proved nothing, since we don't know the relative power of Mr. 1 as opposed to Mr. 2. We can't compare Zoro and Sanji through it.
@Zeefer:
Zoro fought the strongest of Eneru's priests.
Your point? How does this prove him against Sanji? How?
@Zeefer:
Some times when side characters see Zoro in action they'll sometimes question why he isn't the captain, and never the same for Sanji.
The only time I've seen this is recently with the FF. And they've seen a lot more of Zoro than Sanji. And, again, this doesn't mean Zoro has to be stronger.
@Zeefer:
Those are all of the examples I can recall for now. I'm sure there are others that escape me at the moment.
Of course none of these examples are 100% proof positive that Zoro is stronger than Sanji. They just suggest that he is.
Now what about the times it's been suggested they're more or less equal?
Their numerous bouts. Zoro vs. Luffy happens… what? Once? Twice? Zoro vs. Sanji, on the other hand, is in every other chapter.
Their competition in Little Garden. There was no real victor there.
Them teaming up in the Davy Back Fight. It showcased both their rivalry and the tremendous power when teamed together.
Their rivalry in general. Why would Oda show this with no reason?
Of course, the biggest nail in the argument will be in the fights against the CP9. Jabura and Kaku are about equal; it can be debated whether one is stronger than the other, but any argument will likely remain inconclusive... but no matter what, they're close. If Sanji and Zoro face off against those two, it'll be a case where we can make a direct comparison of Sanji versus Zoro.
It's another reason to look forward to the new chapters... I've been arguing about Sanji v. Zoro for the longest time, and this will likely be able to put an end to that argument. I can't wait for that moment...