At Suvarnabhumi
Dawn flights and landings after the rail link has stopped. You can still ride in for the daylight and come back.
The room is the buffer against the road.
BKK · Where to sleep · published · checked
Where to sleep on a Bangkok layover
Sleep on the way you intend to return. A beautiful room that requires two changes and a taxi is the wrong room for a layover.
On the river
The right base if the cruise or the palace is the point. Check the pier and the walk with a suitcase before you fall for the view.
Getting back to the rail link may be a taxi. Leave the extra time in the plan, not in your head.
On the BTS
Phaya Thai is where the airport train meets the BTS. A hotel on that line, Sukhumvit included, makes the return a train you already understand.
Ask for a room off the track if you sleep lightly. The location is the amenity.