Perhaps the most well known of the many premium Bangkok hotels, the Sukhothai is absolutely superb. They have a number of outstanding restaurants including the Celadon which has been voted best Thai restaurant in Thailand. The facilities are excellent with a huge pool, top-notch fitness centre, tennis courts - and they recently opened a spa. The location is slightly out of the way if you plan to spend time on Sukhumvit (and that can be an issue with Bangkok traffic) however if you have to get around during rush hour the train is nearby.