I was just the perfect age when Street Fighter II originally hit the arcades, and I played the original version of it quite a bit (just as I had Street Fighter/Fighting Street before it). I think CE(') is the best version of the game. I know lots of people love Turbo, Super, and Super Turbo, and they are great games, but I prefer the original release line (II, II CE, and II Turbo) best, and CE is the one I like best of the original line releases. There is probably some nostalgia at work, here. I wasn't playing in arcades much when Super and ST came out.
Also, even though the audio doesn't sound as high-quality as the SNES audio, it sounds a little clearer. The SNES audio is too filtered. Meanwhile, the Genesis audio is rather sad and sounds too harsh. Graphically I don't have a preference between the SNES and PCE releases.
So the PCE CE release is kinda the perfect release for me.
Edit: BT, if I may offer a bit of advice: I love your SFII comparison works, but the images on the MAIN page aren't labelled the way they are in the sub-pages, so it's hard to tell which image goes with which console, especially considering you put the images in the reverse order of the game system logos at the top of the page.