Manual. It's like a video game! I find manual keeps me engaged while driving. Works well when driving home late at night and you have trouble fighting the effects of a few drinks, or if you're dead tired. When driving an auto, I can get passive (as one poster says), which means sometimes losing concentration and stopping short, etc..
I think, though, that if I ever start a family and get an SUV, I'd probably get lazy and get an auto. Also auto would be more practical for a big car, no?