Heres a pretty funny video of a XCR torture test.
These guns seem like pretty big pieces of crap. Basically an AK that looks like an AR that is not reliable. Out of your list Id go SCAR. Out of all rifles Id go either AK or AR. Id be happy with either one.
That guy seems way too giddy about a gun that is failing some pretty basic torture tests. I guess he's trying to save face after dropping so much coin on design that is clearly not ready for primetime. Now I wouldn't expect many guns to pass his mud test (pouring mud into an open ejection port is gonna cause a stoppage in pretty much any semi-auto), but I've seen ARs, AKs, and SCARs breeze through similar sand and water tests.