I've done a lot of audio testing over the years, with different audio codecs, different speakers, headphones, etc. My choice? MP3 in VBR, either 256 kbps or 320 kbps. I started with 256 kbps a few years back, but switched to 320 kbps earlier this year. No real reason other than "just because".
Thankfully I only have 88.4 GB of music, so even at the high bit rates I can keep my entire collection on a 120 GB Zune. Of course, that's a dead product now, sooo...
