Closest by road
Really, the distance isn't the issue, it's the trip time by car.
To the hotel:
Depending on the time of day and the motorway exit the driver uses either Westin Grande or Sheraton Grande are closer, but they are literally across Sukhumvit Road from each other.
To the airport:
The Sheraton Grance is closest as when the car exits the hotel, you are facing the right way to get to the motorway. Westin would mean a U-turn at Asoke which can take up to 4 minutes as the traffic lights are red for up to 210 seconds according to the counter.
Sorry to be so pedantic.
In any case, as they are opposite, I like the Sheraton Grande a lot better.