As many others, I liked Lavender Town best (R/B/Y) - yes, of course because of the music, but also for the ghost pokemon in the tower and the sad story about that Cubone and it´s mother.
Well, i like the music of the Pokemon League too.
In G/S/C... Ecruteak City... (surprise...) Because I like the style of Houses, the two Towers and that theatre with the Eevee-Evolution-using-girls. Great music themes in that theatre and in the burned-down tower as well.
[Well... just to complete this... Saffron City is more than nice in both generations, for some reasons... ]