Have you looked at Raffles on Praslin. I haven't been to any of those you mention (bar visiting BT which did look a bit tired), but I would suggest Praslin is a better base if you want to see the variety of the Seychelles and take a few day trips to Praslin itself, La Digue and the surrounding islands. However it doesn't seem from the reviews to be as great an operation as the FS, and it may depend how easily you can connect (by plane or boat) from SEZ to Praslin when you arrive/depart.

Or there's Domaine de l'Orangerie on La Digue which was great but not a par to the others - interesting and cool but not the same privacy/service/food.