Another reason to stay at the SGS or Westin over the ROS is the sky train...
At the SGS and W estin its right out side your door, and for 280 BHT you can get a tourist pass for 3 days unlimited use, which is great if you want to head up to the night markets etc.

Taxis in BKK are a west of time, the traffic is so bad....

I found the sky train very handy...