I prefer using Musepack for bitrates ~180kbps and higher. Gives near transparency.
For 160kbps and lower, Ogg-Vorbis.
Actually Ogg-Vorbis rules in higher bit rate regime too, but it makes slightly bigger files than Muse.
So all people who though mp3 is be-all/end-all, please open you eyes to better codecs that dont compromize on quality and file size.