With business meetings and seminars literally a five-minute walk from the hotel, One One Bangkok was the place to stay for my trip. I had a Deluxe room with a window overlooking the street. My colleague had a Junior Suite, but no window. He said that the lighting made it ok, but being one who enjoys waking up to sunlight on my face, I don't know if I could've done five nights in his suite.
The staff is friendly, although, English is not always the easiest communication method. Early (before 08:00) check-in is not done, but late-late-late (after 05:00) check-ins are OK. If your flight arrives in the wee hours, just book for an extra night so you can take a nap.
The rooms are spacious, the bed is comfortable, and the linens are always freshly washed and scented. The Nescafe coffee maker in the room (along with the complimentary Unfortunately, due to hard water residue, the rainfall shower head wasn't useable (there were two shower heads, the other one was fine).
Breakfast is a choice of three different sets (all served with juice, coffee/tea, and fruit): American breakfast (toast, eggs, potatoes), Jasmine fried rice, or Congee. I didn't try the American breakfast, but the other two were delicious.
All in all, I enjoyed my stay at One One Bangkok, and if you need to be based in the area, it's perfect and quite reasonable.