As someone who's not trying to sell any of them to you, I'd look hard for a Nightforce NXS in your price range, or a SWFA SS 5-20x50 HD model. I would expect either of those to hold up better than any of your list, and the companies to respond quickly if you call them up and say "my 50 ate your scope, can you fix or replace it?" Not that Leupold, Sightron and Bushnell won't take care of you too...
Of your list, the Sightron and Bushie come from the same factory, though obviously made to different specs. The Mark4 is a known item, but the one I owned didn't impress me much (glass was good, it damn well should be for an $1100 scope that is only 3.5-10x40mm and SFP and had to be sent in for service before it was ever mounted on a rifle). I guess I would get the Bushnell if I were limited to your list, but it would be a close call from a purely durability perspective. From a value and features perspective the Mark 4 wouldn't be on the list period. I have examples of the Bushnell ET and Sightron SIII series, both are very well made and have excellent glass, but the Bushnell feels more rugged (with no hard data to back that up).