Hi milgreen2! I spent 5 weeks in Gwada back in 2010 and I can say without a doubt St. Anne is nicer than Sainte Rose. However, I would also add that while I LOVE LOVE LOVE Marie Galante, there's much more to see and do on the "mainland". You may want to consider splitting your time differently, e.g. 4 days on MG and 10 on the mainland with 5 on Grand Terre and 5 on Basse Terre.

The great thing about St. Anne is the fruit market (IMHO). It's a touristy place but the beach is beautiful and you can walk most places depending on where you're staying. You can definitely explore the WHOLE butterfly from just one location but it's really much bigger than it looks and you'll spend too much time in the car. AND, traffic can be bad in some places at some times (the main drag that goes through town can be a parking lot. Staying on each side of the island will give you the opportunity to see so much with less time on the road - and there is MUCH to see.