It's hard to have anything beyond a "flavor of the month" favorite song. Still, while some others currently outrank it in my preferences, it's the songs you always keep going back to that would be your favorite.

Dawn on a Funeral Day - Tsunami Bomb

I've probably listened to it more than any other song, and it finally edged out Hemisphere - Maaya Sakamoto by about 50 listens. It's a good song to drive a little excessively fast to on the way home from work too.

As for right now, I'm partial to anything off the Macross Frontier set of songs, and especially the theme song, Triangular - Maaya Sakamoto.