What's your favorite audio codec?

I recently installed Rockbox on my iPod. For those of you who are not familiar with Rockbox, it is a replacement OS for portable media players. I recommend going to www.rockbox.org for more information. One of the biggest strengths of Rockbox is that it allows a media player to play almost any commonly used audio codec (including FLAC, Vorbis, AAC, etc).

Anyway, what is your favorite codec?