iPod Mini . . .
...which I still use daily. And is also the ONLY iPod I have. I use it for music (and address book entries) only. I keep it running when at work and at home; but if I have to get up and walk around, it's very convenient. I have no accessories that it didn't come with. I do use a utility to move music from the iPod to the Mac - a great benefit (thank you to the developers, who have been paid).
It is not the model per se of the iPod that qualifies it, but the software and hardware, and Apple's attention to the end user by keeping in the development loop and updating the iTunes software consistently.
PS: I didn't buy it; I won it in a contest. It was only after I started using the iPod that I realized what a huge benefit it was for me. Had I known, I would have bought it. What a great little innovation. Kudos to Apple for being prescient enough about the music market to develop such a great product, and in iTunes, such a great marketing advance.