Maybe I'm using the wrong word. I think the right word is counterpart. Yeah the two pirate groups are counterparts.
(Here's a thanks to Ubiq)
Zoro VS Lafitte
Similarities:Both are second in commands. Both served as a form of law enforcement. Both had been known of prior to joining their respective crews.
Differences:Zoro is stern and fairly dour while Lafitte is cheerful and hyperactive.
Ussop VS Van Auger
Similarities:Both are the snipers of their respective crews. Both are skilled marksmen. Both have eyewear.
Differences:Ussop believes that you can make yourself strong as long as you try hard enough while Auger believes that a person is only strong or weak because of fate. Ussop has a slingshot while Auger has a Musket.
Chopper VS Doc Q aka Quelch
Similarities:Both are doctors. Both have a relationship with animals. Both are fairly skilled medical wise.
Differences:Quelch is so "weak" that he can't even stand. Chopper is kind and gentle while Quelch is extremely cruel as well as possibly somewhat violent. Also their respective relationships with animals are different.
Does this make sense?