Easily the C64 version, great graphics, superb music, what more could you ask for? (i'd have liked to have seen a C128 version, extra level over C64 perhaps?).

Speccy has some nice sprites, but they 'merge' with backdrops making things confusing and (48K?) sound is a bit tragic.

CPC, decent music, colour, but that opush scrolling, sparse foe count and general chunky look pushes it into third.

I have to defer to a Speccy-owning friend of mine who said to me after playing the C64 version, while very good, is a tiny bit sluggish control-wise compared to the slick Spectrum incarnation.

He is very non-partisan, so I take his word for it. Me though? I'm no fan of G'n'G. I do like Demon's Crest (because it's colourful, has gorgeous music and is a fair bit easier than this).

EDIT: managed to leave a word out. As I often do. As well as doing small sentence fragments without an active verb that irritate grammar checkers.

C64 in this case.
Something very rare: The music is completely different from the arcade in the C64-version, they did not try to do the same tunes; instead they did really excellent new music. Even more memorable than the original to me.

The talk of the Commodore 16 version in another thread made me go looking, I wish I hadn't 

http://www.youtube.com/watch?v=WH6xhBPkx5Y

The talk of the Commodore 16 version in another thread made me go looking, I wish I hadn't 

http://www.youtube.com/watch?v=WH6xhBPkx5Y

Me and my big mouth....

That is pretty bloody shocking, no wonder it got slamned at review.They must have been able to knock out something better than that, could'nt they?

The icing on the cake there is that they've ripped the original colour sprite out of the C64 preserving the original double-pixel bitpairs (00, 01, 10 and 11) in the data that tell the VIC-II chip which colour is supposed to be displayed, but simply made it monochrome so you get this malformed, ghostly blob instead of a proper sprite. I mean it's almost understandable that there's no animation due to the memory constraints of the C16, but there's no excuse for the laziness evident in the main sprite.

Oh wow i loved this game on the MD.. Never played any other versions..