For more info about Ogg format see this thread:
http://www.aximsite.com/boards/showthread.php?t=60086
I decide which rate (64, 128, etc) to record at depending on the type of recording I am doing.
If it is just vocals , I go with a lower rate (64K or even less). If music, I use 128K.
I don't notice much of a difference when I go higher than 128K, so for me, it's not worth wasting additional drive space, to step up to 160k or higher. To me compact music formats are meant to be small, so I can carry a lot more songs with me on CD's and storage devices. I can listen to my original CD's if I want them to be absolutely perfect. But I really can't tell much of a difference between an MP3 at 128K, and my original CD. So 128K is fine to me.
I just recently started using the Ogg format, as mentioned at the top. I recommend viewing the thread link provided above.