Dang. People do not understand SFII very well...kind of amazing considering it was THE game for a couple of years.
A few things:
There are five versions of SFII. The most popular one today is Super Street Fighter II Turbo (aka: SSFIIX) which didn't even get a 16bit home port. The PCE version is SFII': Champion Edition which was the least significant upgrade Capcom made. It allowed two people to play the same character against each other and the ability to play as bosses. It also had minor ballence tweaks but it needed a LOT more. I am not one to complain about ballence AT ALL in fighting games but this this is crazy. Furthermore, its so slow that all the unfair shit like re-dizzy combos are really easy to pull off.
All 16bit console ports are letterboxed and have resized sprites. This is partially related to shrinking the ROM size but also because Capcom's CPS systems use a weird resolution. Ask JapJac about that.
All versions have f*cked up sound, including the arcade. What I mean by this is that they all sound like the system they came from. As shitty as the Genesis sounds, it's more in line with the arcade version, and late 80s/early 90s arcade sound in general. The SNES version is much cleaner sounding but more it's own sound than the arcade sound. Etc.
All OEM controllers sucked for SFII so bullshit comparisons between Avenue 6 and SNES or whatever are pointless. It takes an act of God to achieve a decent combo on any of that crap. While Sega's six button is probably best, and Sega's three button the absolute worst, the real choice back then was a stick from Hori, MAS, or someone else.