The Amiga version was closer to the arcade than the Mega Drive version, the only thing letting it down was the lack of a jump button (which could be fixed in WHDLoad soon anyway, they've already added an extra button for magic). The Amiga version, although different to the arcade, had a nicer colour palette. It has better music, more background graphics, and was more faithful to the arcade version overall. The only thing the Mega Drive version has over the Amiga version is the jump button, and perhaps a closer colour palette to the bland looking arcade version.
Here they both are next to the Master System version.