The short version
Ratchathewi is central Bangkok with very little wasted distance. Phaya Thai, Phetchaburi, Pratunam and the canal all sit close together, but they do not feel alike. It suits someone who wants quick access to Siam and several rail lines, and who can accept crowds, hotels, traffic and a shortage of quiet domestic streets.
The address matters
Around Ratchathewi BTS and Phetchaburi Road, towers and transport dominate. Pratunam is intensely commercial, with wholesale activity and visitors. The lanes towards Makkasan and the canal are less polished but can feel more residential. A room facing a main road may trade a short commute for constant noise.
Getting around
Ratchathewi and Phaya Thai BTS stations, the Airport Rail Link at Phaya Thai and the MRT connection at Phetchaburi make this one of Bangkok’s best connected central choices. Walking is possible between some pockets, though crossings and heat make short trips tiring. A car is unnecessary for most residents and awkward around Pratunam.
My verdict
I would choose Ratchathewi for a compact city life, especially if work or study is central. I would not choose it for greenery, silence or easy weekend parking. The right building can make the district exceptionally convenient. The wrong one puts you above a traffic queue and beside a hotel lobby.