If you can, use 192. Above that makes virtually no difference, using 192 is the best mp3 gets, there or thereabouts. Generally it's a question of file size/storage space. If a mix saved @192 doesn't cause you problems in terms of storage, go for that, since the download time (although slightly longer) I do all mine @160 because I've got quite a lot on my site and I traded off a bit of quality in order to be able to store more. Failing that 128, but there is a noticeable difference between 128 and 192. Compress the mix before you convert it to mp3 if poss, that also makes a big difference.
