Last week I stayed at the Le Meridien and the W. Previously the Hilton Millenium, the Shangri-la, the Royal Orchid, the Dusit Thani, the Renaissance, and, in earlier poorer years, a variety of others. No hotel took better care of me than the W. The Le Meridien is very nice, very comfortable. The Shangri-la was a wonder. The Dusit Thani is closing, and I have nothing very good to say about the Royal Orchid. Neutral on the Renaissance.
Given the nice room, and the very personal attention, the W would be my choice in Bangkok.