We stayed in Flic en Flac, near Wolmar on the West Coast. Its a pretty small place but travel by road can take a while. We hired a car and covered most of the southern half. Lovely place.
I dove with Sun Divers, based out of La Piroge hotel in Flic en Flac. They were good, pretty good dives sites, decent equipment and quite a busy school if you are looking to do some courses. Its particularly good if you like undewrwater photography as Gerald (owner) is very good. Couple of points though: The dive briefings were not always very good, and the DM's often spent alot of time photgraphing things which was a bit dull if you arent into photography - I sometimes felt all I was doing was funding their hobby! Overall though a safe outfit and a laid back, friendly approach. If you do visit Mauritius, Id recommend Cassella Wildlife Park (you can walk with Lions!) and also there are some great waterfalls in the region.