Versions that are bad
Anything that says Domark on it. ANYTHING.
ANything that says Virgin on it.
The SNES version is amazing, but not the original game.
Here is my list of versions worth playing
perfect: Apple ][, Amiga, DOS, Mac, C64, SNES (but it's not the same game).
Very Good: PC9801, Fm Towns, Sega CD, Sharp X68000. While these are not "mod perfect", they are VERY close, and play wonderfully. Two tile running jump, failure to grab after falling too far, and warp glitch all work. Normal speed in these version is three, but they are playable on speed 1 (fastest). Any of these version are definitely worth playing.
Not Bad: TG-16 CD. They tried, but since they had to reprogram the entire engine for an 8 bit CPU, they kinds screwed up a few things. But it's fun to abuse the ledge grab bug and speedrun level 8.
Sam coupe is impressive for a totally unofficial conversion. Worth playing still i think.
Avoid:
Atari ST. Looks very nice, but framerate is wayyy too inconsistent.
NES. You don't even merge with shadow! FAIL!
Genesis cart: Domark. need I say more? HORRID controlls, you can't two tile running jump, etc.
SMS/GG: again crap controls.
Gameboy: sadly this is better than NES, but the game really needs a bigger screen.
Possibly worth a look.
Speccy, CPC versions.
If you must play only one version, make it Mac, Amiga, or MS-DOS. mac is best, but it actually requires a real pre-intel mac to play right. If you must play only two, the second version should be SNES. If you like 8 bit, play c64 version, as it's mod perfect. Apple ][ version was awesome for it's time, but we have better options now.
Sega CD version is probably the best out of Japan besides the SNES version , as it got an uncensored full english release, and still has that solid play control. If you don't care about that, then the other very good versions are quite good. And, if you happen to have a turbo duo, play that version, as even with it's bugs it's still pretty playable.