So far, the only two versions of the M!X are the Spacey and Melody versions, yes. There was a video a little while back in the thread that showed Spacey Land, but I don't think we've seen Melody Land yet (at least I haven't). It'd be best to go back and look for the video (it shouldn't be too far back in the thread), but basically there were a lot of bright, neon colors, a night sky backdrop (I think?), and metallic buildings that looked like they were made out of spaceship parts or something. It was really cool! Definitely flashy, though, so if that isn't your style, maybe Melody Land has a gentler color scheme.
I mostly went off the exclusive characters of the version when I chose a blue spacey version, though, since personally I think the characters will have more of an impact on gameplay.