I am very fond of the Royal Orchid Sheraton in BKK.
It is on the river (which I prefer). It is a little bit out of the way from the business areas, but it is very convenient for renting a canal boat next to River City Plaza (not a bad shopping area).
The rooms are very nice (the suites are delightful), and the service is charming. The Oriental is a better hotel, hands down, but the Royal Orchid has a big price advantage. Ever since Sheraton opened the Sheraton Grande Sukumvhit, the Royal Orchid has been the #2 property with a good price break.
It is a little older that the other top end hotels, but I have a strong affection for it.