16" load G S637 Sailuns has been around first as the LT tire and debadged as a ST since the '10 era. I have the LT E Sailun G S637 on a tri axle GN trailer for over 6 years now. Great tire at any speed at max loads.
The 16" load G Westlakes have been out around about 2 years now and are popular on haulers websites and some rv website forums for heavy trailers. However like Goodyears new Endurance they simply haven't been around long enough to determine anything other than their made in the USA therefore popular.
I would run the Westlakes.