Which Religion would each of the Straw Hats have?
They're all agnostic.
Remember when they found that barrel before Thriller Bark?
Nami definitely believes in gods
Zoro definitely doesn't
Rest of the crew is unsure
Usopp wouldn't risk not believing in gods
Luffy only does it out of fun
For Robin it's just a thing of customary
She just suggested they should pray after looting the sea god offering. I don't think she was even serious. Based on their actions, her and Ussop are at most "superstitious."
Nobody on the crew seems to give any consistent thought to a deity. They're all agnostic.
Sanji seems to ponder about God when he sees a miracle like in Logue Town
Bellemere's grave is a cross