User blog comment:LuffyPirateKing/Zoro or Sanji??/@comment-3242083-20110113221236

They are almost equally powerful, Zoro being minimal "stronger"(if at all). Sure, it is clear that Zoro always fights the second and Sanji the third strongest enemy, but in the CP9 Saga we got a nice hint as to how big the difference between 2. & 3. really is (thanks to douriki):

Kaku, arguably the second strongest member, with a douriki of 2200, fought by Zoro.

Jyabura, the third strongest member, with a douriki of 2180, fought by Sanji.

The difference in power is 20 Douriki, the strength of two  average "cannon fodder" marine soldiers. The difference in raw power, by that logic, is thereby 0,909 percent.

That said, a difference of not even 1% will not make or break a fight. You would have to consider the stage, luck and determination as well. Especially the latter will probably be decisive.

My prediction if it would ever come to a battle: they collapse both after a few days, similar to Jinbe and Ace.