We just did an overnight in Bangkok to review the new Park Hyatt. Arrived at about 4pm - felt a bit tired so decided to get an Uber. 1hour and 48 mins later we arrived at the hotel
Strongly recommend getting the train!
Personally, our favourite luxury hotel in the city is Sofitel SO. Location and price are excellent, along with an awesome infinity pool looking over Lupini park.
If you decide to stay at the airport, the on-site Novotel is actually very good too. We have stayed a few times and particularly like the courtyard swimming pool with swim up bar!