In theory CBR 320 kbps is better quality, since it's the highest the spec supports. In practice you're not going to hear any difference unless you're some freak of nature.

CDex<BR>Lame V1.32<BR>44khz<BR><BR>WAV file - 88.3mb<BR><BR>min:96kb/s <BR>max:160kb/s<BR>q=0<BR>VBR 0<BR>9.9mb<BR>VBR 5<BR>9.5mb<BR>VBR 6<BR>7.3mb - good quality ...