Commodore 64 Though I eventually got my own C64 virtually at the end of its commercial life (1993), I had previously seen it as the only computer I should have owned above all others (despite the fact I was familiar with the Amigas and IBM Windows PCs).
The C64 was the first machine I explored and used to hack games, program and generally use as a jolly decent office tool and cheap games machine. I still have all my old games and files, now ported to CD Roms for emulator use.
These days, due to its bona-fide synthesiser, I use two Commodore 64s as part of my recording studio kit. They act as my MIDI composer and keyboard machines which link up to external MIDI syntehsisers, VST computer and mixer.
A real king of a machine, still truly useful years after its official 'death'.