I preferred my 3G, but left it outside in the rain and killed it forcing me to upgrade to the iPhone 4, which I've had for several months now.
TS, I'm intrigued on your definition of retro, could you elaborate? I don't think the 3GS is considered retro in design...
The iPhone 4 is sexier.
I honestly prefer the 3GS's design a lot more, I don't know why. I just kinda like how it looks a bit retro but still retains a futuristic look. If I could have a 3GS with the retina display and front facing camera, I would take it in a heartbeat. Am I the only one?
I think the iPhone 4 looks classier, but I'm not a fan of the glass back, which essentially doubles the chances that a fall will result in a crack, nick, break, etc.