Hello Frank
For portable players 128 is fine, for listening to the sounds on a normal system don’t go below 192, and if your using high end sound samples (Colossus, Giga samples etc) then anything less then 256 will be noticeable.
Remember also that the higher the bit rate, the larger the file becomes, so you may need to choose a balance.
BTW. If you can use WMA files then you can use a lower bit rate for the same quality of sound, (IE 192 becomes 160) and this will also give you smaller files.
Hope this helps.

Bill