Be careful what you wish for, there is absolutely nothing to do on Mustique but sit on the beach, have a drink at Basil's Bar and browse the small convenience shop and getting to/from any other island is difficult and time consuming, at best. Mustique is best described as a private island enclave of high end villas for the rich & famous - there's nothing else there. It's very small, you can drive around the island from one end to the other in a Mini-Moke (think motorized golf cart) in under15 minutes.

Canouan is not that much better although it is a somewhat larger island but still not much in the way of "things to do" - a little hiking, a few water related activities and perhaps some fishing and sailing.

Consider these destinations only if your group truly wants to "get away from it all".

Have you ever stayed on St. Barts? Comments?

gocaribbean.about.com/od/hotelsandre5/tp/Stbarthstophotels.htm
WAY better choice like Carl Gustaf Hotel and Victoria's food
Beautiful flight in sort of bracing airport VERY short but
great beaches vibestyle and french food.

What I like about Canouan over Mustique is the ability to take day trips around surrounding cays, it's a lot harder to do from Mustique. Especially Tobago Cays and Mopion, they're stunning!

Agree with qwovadis - St. Bart's has lots to offer. You can rent a villa there that will house your party and you'll have all the privacy you need plus access to all types of watersports, some of the best shopping in the Caribbean and, without a doubt, many of the best gourmet restaurants in the Caribbean - many rivaling those you'll find in Paris.