What smartphone should I get?

I want to get a new phone, but I'm not quite sure which one I want to get. I'm looking at a few android phones like the Nexus S, the new Samsung Captivate 4G, the HTC Desire HD, or the iPhone 4. I really want a new phone and don't mind paying for it. Or should I wait for the iPhone 5/4S to come out and get that?