I voted Commodore 64, but my first machine was actually the Commodore +4. Weird little thing, 64k of memory but compatible with the Commodore 16. Seem to remember it was only on the shelves for about eighteen months, if that, and then got shelved.
Played about with this for a couple of years, wrote a lot of very bad BASIC programs on it, then it went to the great hardware place in the sky and we upgraded to a Commodore 64 which seemed to be mentioned more in the few computer books in the local library, and also had the nice feature of having more games.
Now I'm getting tempted to try and get a +4 emulator and see what kind of thing I can write on it given my somewhat greater computer experience. Think somehow it'd drive me crazy quite quickly though so maybe one of those things best left as a vague concept.