Great question.
First, OGG is superior to standard WMA @ 192kbps. However, it's not compatible with too many things out there and seems to be loosing popularity. Whatever CODEC you choose, you probably already know that the higher your kbps setting is, the higher the sound quality.
I use to rip my music as WMA lossless and sync at WMA 192kbps. However, I'm finding better results by copying and pasting mp3 320kbps at files directly to my SD and CF cards without any conversion. They seem to be a better space compromise and are not as compressed.
If you want the best results, don't buy your music on-line. It's only available compressed. I buy CDs as they're still the reference fidelity. I buy a lot of them on ebay and other alternative places.
If you have the hard drive space, rip it in WAV and sync AAC for your device. betaplayer supportss AAC files and AAC is the best CODEC out there right now.
WAV is not a CODEC as it does not compress the music. It simply makes an exact acoustic copy.
Um, sorry about the long post.
http://www.bestmp3guide.com/
http://www.dapreview.net/news.php
http://www.hydrogenaudio.org/forums/index.php
http://www.vialicensing.com/products.../standard.html
http://mp3.radified.com/
Mike