Well, if you really wanna discuss this, just take a look over the latest prods in the demoscene, and you'll figure out the capabilities of every system...
Under my point of view C64 has the best multimedia overall, followed by the 800/XE
Back in time i owned a C128, till i fried it, (yep me too). However despite i found i had the fastest computer in load times, with probably the best audio chip, and with great gfx features i always found game conversions what were real crap. Plus the Basic for C64 was really difficult.
Always got jealous about the Speccy because its huge amount of releases, but always reminded either it was far behind from the C64 in video stuff, plus to load something from cassette was a pain in the neck, all games took much longer to load. Got jealous about the CPC gfx palette and Hi-Res mode. And got jealous about MSX japanese catalogue, and Basic. Plus jealous about 800/XE CPU.
However, i feel C64 got the best overall, despite its flaws. If you disagree, just dig into youtube or pouet.net for the LATEST demos for every system you want to compare. You'll notice i'm right.