I had a few iPods already. Upgraded from a 4th gen. iPod (there were no different iPods back then) to a 80GB classic. The Coverflow wasn't that great, because of the hard disk, but I had lots of space and longer battery life.
Then I bought an iPhone and got into the trouble of not knowing where to keep the music. The iPhone of course was too small to have all music with me. But I did not use the iPod that much now, so I decided to give it to my girlfriend and stick to the iPhone.
Two weeks ago I bought the 160 GB classic.
I really enjoyed carrying around only one device, but the iPhone did not have the best battery life, the sound was only well and nothing more and I always wanted to listen to music I did not sync before leaving the house.
Short: the Classic.