I would say the shrimp since it seems like your tank is going to be pretty full. Cories likes to be in shoals, and once you add those to the rest you are running into an over stocked tank. I think Cories are a little bit more compatible with Bettas though. I've read of shrimp eating the fins on the Betta, and of bettas eating shrimp!
Good luck with whatever you choose, and as always, post pics!