If I meet a famous person, and assuming their music is of great importance to me, I'll say something like "Man, you and Rush are my favorite bands, ever!," or "I loved your new album!," or "Born to Run is one of my favorite albums ever," or "Your music sucks now, but hey, we'll always have Quadrophenia!" As a fan, I would be careful not to show ranking of their music, but to show that their music is resonating. Lots of people would still take the "you're number 2" thing to be criticism, so omitting it completely might make their day better.
If I were a famous musician, I personally wouldn't mind, be flattered that people enjoy it, and plot to kill the number one bands.