I used to play the SNES version, it was great. Amiga looked better i guess, but lacked music tracks. Other versions are far behind.
SNES and MD ports are quite similar, but MD has worse audio.
Amiga has better gfx than SNES and MD versions but has no music.
ST version is quite similar than the Amiga version but with less colours and worse audio.
Acorn version looks like to be a perfect match of the Amiga version.
About 8bit versions the only remarkable one is the GameBoy Colour version. C64 has nice playability but awful gfx, CPC and Speccy have better gfx but monocrome mode, and less playability than C64 version.
So if would say there's a better version of SWIV has to be the SNES version, followed closelly by Amiga-Acorn and Genesis ones.