I prefer PC Captains, hell, if I have to I'll just make up a few NPC's for the vacant spots and they can conveniently die in a house fire when someone wants to take on the role :P
I just think it's hard to keep all of the Captains NPCs. Especially when the captains will probably have a big part in the upcoming arcs.
I'm happy for no limit on characters, but I agree with MysT3CH, if someone isn't that active and have 5 characters, it'll be a disaster.
On a completely unrelated note,
Has anyone ever thought about how the writers of massive anime shows like Bleach come up with their content?
I so wouldn't be surprised if they stalked sites like this and just adapted the plots to fit the characters.
I don't know, just a random thought that popped into my head :P