I may just luckily pick the days that are not very crowded, but I have always found Pinel to be a relaxing, quiet beach day. Plus, I find choices at Karibuni that are not frequently available elsewhere at lunchtime on the mainland of SXM (ie- trunkfish). While the snorkeling on SXM is not all that amazing compared to other islands, Pinel is probably the best it has to offer (other than Creole Rock).

If able to get to Pinel as part of a private day charter or daysail, it is even better, since you can come and go as you please, rather than relying on the water taxi.