My favorite old computer had to be the Commodore 128. Basically it was a C64 with twice the ram, and twice the Basic commands (though it could emulate a C64 perfectly, and that was its downfall.) I've never since found a way to do three (not, four) sound voices at once, or to make sprites that moved without any CPU intervention. My PII may finally be fast enough to emulate that kind of sprite in Visual Basic (but I doubt it!) I even dabbled in assembly language a little, and got the fastest (smoothly) moving sprites you've ever seen with it! Edit: Did I mention the dual-monitor capability?
Of course, not everything was fast about the C64/128. Drawing a 50x50 Mandelbrot set took 15 minutes at the "fast" 2MHz speed. Most of the programs on that machine either I wrote, or I got from old issues of a British magazine, Commodore Disk User (on disk, of course. ) But I do remember typing in part this planetarium program, probably the only program I ever manually entered, during President Clinton's inaguration (hey, I was 11 or so and I got bored.) It took like 8 minutes to plot a simple patch of sky. :Q
My parents still have the C128, BTW. I hear there are C64 emulators available for PCs, but everything I'd want to run now I wrote for the 128.