Title basically.

I remember playing three version on three friends consoles when I was younger. There was the PS1, N64 and Dreamcast version. The Dreamcast version was the best one, heads and above the other two and I'd definitely prefer that one (Better graphics, sound, etc)

The store page doesn't specify which version this is, anyone know?

There was also a PC version, and that would be what GOG has. It's more or less the N64 release but with better graphics and sound, but no other major changes that I know of.

It's the original PC version. Has the same content as the N64 one, but with better graphics and sound.