The PCE version of SFII' is a superb conversion. The graphics look more vibrant and clearer than the Genesis version and even sort of better than the SNES because of the reasons NEC Avenue mentioned and even the mature thing RCduck7 mentioned. Not only are the graphics top notch, but the sound is terrific; music, sound effects, and voices! I haven't played the SNES version in awhile, but I loved the music in SFII' for the PCE more than the Genesis version.
Also I found out that the PCE version even fixed this annoying gameplay problem. I am normally used to play Super Street Fighter II on my cousin's Genesis, so I'm not sure if this is in the other versions, I'll have to try checking it out. Anyways, if you Bison (or Vega as the Japanese versions) and do a psycho crusher, you have this incredibly easy chance of throwing the opponent if the opponent blocks the psycho crusher. In SFII' for the PCE, this problem seems to be fixed, which is great because that throw was so annoying and unbalanced the game a bit.