If you are willing to spend the money, the Ritz-Carlton is the nicest. I got a free weekend stay there a couple of years ago becasue they left me and my family at the airport for 3 hours when they kept saying they were coming for us. The service and even the basic room are unsurpassed by any other chain hotel, in my opinion. Also very nice is the Hyatt Regency, though not nearly as expensive.