I'm finding it hard to remember my fave C64 games. I keep recalling games I loved and they are mostly Spectrum games. (Starquake, Bruce Lee, Cyclone, Highway Encounter, Knightlore, Alien 8, Atic Atac, Elite etc). Yes, I know lots of them ended up on C64, but I fell in love with them on the ZX.
When I got my C64, I was more into the music and learning programming etc.
I did really love Leaderboard though. Had a bit of a thing for Zolyx and play Great Gianna Sisters quite a lot. Mostly though, the games I liked were probably for the music for the majority of the time.
I don't know if this revelation is a bad thing, but it's a fact. I'd never be without my C64 though. I can do stuff with it other than just load and play a game and that has a great deal of appeal.