The “Siam” area is right in the middle of things. It's still the main shopping area of Bangkok, as well as a major transportation hub, where two of the city's rail lines cross. However, staying in this area doesn't mean you're stuck with tourist class hotels. You're spoiled for choice no matter what class of hotel you're looking for.
At the top end is the luxurious Siam Kempinski, along with the Grand Hyatt Erawan and the InterContinental. A little further down the scale, at four stars, are the Mercure Bangkok Siam and the Novotel. Other places to consider: