+1 for Renaissance Bangkok Ratchaprasong
You cant go wrong with that one.... But check if they have a promotion running.. not worth to use the awards if they run a promo for ~3000thb...
There is also a new cat 4 Marriott opening this year in Thailand at the east coast. Marriott Rayong... not really much information around yet.
Just paid over $200 USD per night at the ren bkk. It was 5500 baht ++, ended up costing about $220.
Also great if a hotel opens up in Rayong. I believe Rayong is between Pattaya and Bangkok, but closer to Pattaya.