I was a little annoyed that the interface for MTVMG2 was so different, but it didn't take too long to get used to it. I prefer hard rock/heavy metal and the guitar sounds in MG1 weren't all that "real" sounding for my tastes. Using MG2, I was able to get more realistic guitar sounds - not completely real, mind you, but more real, nonetheless.
All in all, I'd say that they both have their good and not-so-good qualities, but I did prefer MG2.
MG3? It looked to be more about just remixing someone else's songs and less about being creative. I never even bothered with it.