These are the computers I have owned as new purchases, not including computers I've collected and tried.

1983 : Oric-1

1985 : Atari 800XL

1988 : Commodore Amiga A500

1992 : Commodore Amiga 1200

1995 : IBM PC

I still own my original Oric-1 from 1983.  It's important to me for nostalgic reasons but I think the Atari 800XL and Amiga A500 were my favourite machines because the hardware design was so excellent. I didn't know it at the time, but turns out that both of these machines were designed by the same person - the late but great Jay Miner.