Hello and Welcome to Apple Discussions.
It does depend on what device(s) you intend on playing the music on.
For storage on hard disk and burning to CD later using AAC at 128kbps would be a good compromise. There is some quality loss but my ears can't tell the difference. Why not import the same file a couple of times and try for yourself.
For AudioBooks you can use a much lower bit rate and the quality is still acceptable.