If I was going to be a theist...

I would be a pagan. And not one of those modern neo-pagans, either. I mean worshipping a pantheon-- the real deal, which probably doesn't exist any more. Unless you count Hindu. That's more what I'm going for, but I'd go with Roman "myths" (i.e., religions that nobody believes in anymore) because I've got a lot of Italian ancestors. So ritual sacrifice (but no human sacrifice, please), seasonal celebrations where we really do get drought if we don't do it right, temple prostitutes, the whole deal.

Another possibility is Catholicism. There you've got your trinity, your saints, your mother of god, you can pray to them all. And loads of religious festivals, especially if I move to Central America or something. But it would be a shame to lose out on temple prostitutes.