Although I would rank qasr al sarab as no. 1, I think u should try banyan tree as its almost as good as QAS ( go for the beach front villa) , and much closer in terms of the drive. Barely took us 2 hrs to get there whereas QAS was a 4 hr drive . Desert island resort is great if u hv children as it has many activities and u may also find it beautiful if I haven't been to the previous 2 mentioned. Personally I didn't find anything exotic about the resort ... Just made me feel I'm in Thailand ;). Good luck with whtever u decide
