XD There are a lot of these kinds of topics nowadays..
Crew members:
1. Luffy, well he is Luffy... he beat all of their strongest enemies and he gets the usual main character power and he always improves A LOT. Unlike most who just improve a bit in the midst of a battle or just show off their best attack when they're about to lose.
2. Zoro, it's always implied that Zoro is stronger than Sanji but it looks as if they're about equal but I'll go with the "facts". He usually defeats the second strongest person on the enemy side and he doesn't avoid battle so you could see that you could see his strength.
3. Sanji, like I said above, they should be about roughly equal in strength but since the author doesn't show Sanji in very important battles we could just wait.
4. Chopper, with his whole triple Rumble ball thing he just destroys everything but even just with one he seems more superior than the rest.
5. Franky, this is where it starts getting harder. I'll just go with Franky since everyone else under him hasn't showed any superior fighting capability than him (except maybe Nami's fight against that woman with the bubbles and that other woman with claws).
6. Brook, I'm not sure but he seems pretty good with a sword so I'll leave him here.
7. Robin is obviously strong but she doesn't fight much so we could only assume it's because she is either rather weak or just doesn't like to fight. By the looks of it, she isn't much of the one on one battle kind of person and more like a supportive fighter. She usually only kills people who aren't strong since the main thing she does is break their back with her numerous arms (which honestly freak me out sometimes).
8. Nami is only better than Ussop since she got the weather staff (forgot the name of it, it's been a while since it was mentioned) and beats a lot of strong fighters later on.
9. Ussop is a sniper and uses cheap attacks. Like when he was against Luffy, he only had a chance because he knew him very well. If not, he would've been destroyed in a few seconds.
Well they haven't shown/ I don't remember most of their strength so I won't list them.