Of the choices you listed I have only fired/handled the SCAR and the FS2000.
I would chose the SCAR between the those 2.
The SCAR has easier to use controls, isn't a bullpup, and has seen more use in actual combat than any of the others.
I have heard bad things about both the XCR and the ACR that would preclude me from considering either for a serious use rifle as well as the fact that neither has seen any combat usage.
As to why combat usage is important, the SCAR series is on something like iteration #7 based on feedback received from testing and combat experience. There are things that can't be replicated in the test lab that show up in real life usage.
I, like Fishbed77, chose the AR.
I am no longer participating in gun forums.