Luffy - agnostic, doesn’t know or care
Zoro - militant atheist, pisses everyone off who tries to discuss the monotheistic view of God
Nami - Christian, clings to a higher power to cover for her own shortcomings
Usopp - Jewish, big nose and a cowardly liar (any of you who agree are anti-Semites)
Sanji - Muslim, I don’t fucking know, this is a tough question
Chopper - Satanist, see above
Robin - Hindu, I liked MugiwaraMaster’s answer
Franky - Scientologist, loud and obnoxious because he has no actual beliefs
Brook - Catholic, holding on to his guilt over something that happened decades ago
Jinbe - believes that we’re all just energy, man...from stardust we come, and to stardust we return