Bangkok has the best range of restaurants in Thailand (and probably in Southeast Asia), with food from all over the world and all types of prices. The recommendations that you find in each section are essentially around Silom Street, Banglampoo or Sukhumivit as most visitors will be staying there. For Chinese food obviously Chinatown is a good area to explore. Pahurat (and also Bangrak) is a good area to try Indian food (thanks to the Indian population). Western food you find especially around Silom and Sukhumvit area.