128kbit is normal cd quality, diff software used diff sound quality. Anything above 128kbit is considered oversampling, the quality is sure better than 128, but sometimes it will become 'unreal'. 2 software that I used so far is Creative and Musicmatch Jukebox. This 2 programs can give a good sound if compare to others. But compare to original CD still mp3 will be the loser. So the best is rip it between 192 or 256, it will be the best.
As some of us might be downloading mps from Internet(illegal) the quality will be 96 or 128, very rare to get 192 or higher due to file size is bigger. Some people might think convert 128 to 192 then will get better quality, this is not true, as video, picture and songs can be downgraded but cannot be upgraded, if can also it will be minimum.