I used to always say it was a Tie between Silver and Emerald, but now that I'm Replaying through Diamond I need to give it the credit it deserves. Most of us have overplayed that game to the point where the music is a blur in the back of our minds. However, if you go back and listen now, after a long break you really appreciate the catchy and lovably tunes in one of the most played pokemon games to date.
At least, that's how I feel.