I spent a layover in Miami at the Colonnade hotel, an older classic hotel with modern Westin natural touches. The hotel itself was beautiful and very convenient to the airport without being in a seedy location.
My only complaint is that I had to argue my way into an upgrade even as a Platinum SPG member, but eventually they put me in an amazing duplex suite on one of the top floors.
The staff was very friendly and went above and beyond. I forgot my breakfast voucher at the front desk, so I called to check about it and before I hung up the phone someone was at my door with it.