Will be spending a long weekend in the Miami area; just basically want some R&R. We are considering: Mandarin Oriental, Sheraton Bal Harbour, Sonesta or Ritz Carlton Key Biscayne. What do you think?

All of them are excellent. Ritz in KB and Sheraton Bel Harbour are water front and more attrative things around. Mandarin has great view and ratings but area is quite quiet on weekends, mostly business area.
Great shopping accross from Sheraton, very relaxing surroundings in Key Biscayne.

Just realized, our return flight will leave MIA at 830am so which of these would you recommend based on our having to be at the airport at the crack of dawn?

I don't think that extra bit of information makes much difference.

If you wan the beach then obviously the Mandarin Oriental is not for you, but if you'd prefer quiet luxurious solitude as opposed to a bunch of families in a resort atmosphere, I'd vote for the Mandarin as being the best of the choices -- and I'd love to have dinner at Azul there.

Rits KB is about 30 minutes drive to airport, with a flight at that time, traffic should not be a problem..Time from Bal Harbour should take about same 30 minuts, maybe little more....
Mandarin is much closer to airport

Thanks for your input. Also might consider something in Coral Gables or Coconut Grove. Any suggestions?

coral gables is my favorite place in south florida. nice for walking around , lots of restaurants and a brand new shopping center, merrick park. the biltmore hotel is excellent, no hotel beats the swimming pool, in downtown coral gables there is a nice hotel, corner of ponce de leon blvd and miracle mile, can not recall name right now, but very nice. lots to see in coral gables. venetian pol is incredible, nice to drive around neighborhoods and see all the mediterranean beauties.

The nice hotel in downtown coral gables is the omni colonnade...excellent