Just completed a 5 nights stay with my family of 4 in Bangkok.
We like Bangkok and have stayed several times before in The Siam, Capella and MO.
This time we had booked MO for 5 nights. (This was a city shopping stop in between Bhutan and the Maldives)
Last minute we decided to give Aman Nai Lert a try for 2 nights. So in the end we stayed 2 nights in Aman Nai Lert followed by 3 nights in Mandarin Oriental.

The difference in service, hardware, convenience of location, food&beverages was huge. After staying in the new Aman the MO felt like a Sofitel. So don’t do what we did. Either stick to your current best option ( Mo, Siam, Capella are all nice.) Or if you don’t mind spending a few extra $ just book Aman Nai Lert, this is imho currently the best hotel in Bangkok without any close competition. Don’t mix your stay though ☺️