As was mentioned, the top pic is the factory muzzle brake that comes with all SCAR 17S rifles on the civilian market.
Personally, I think the SCAR looks cooler with the AAC MITER flash hider (the 2nd pic) - after I bought my SCAR, I removed the factory PWS brake and installed the military issue AAC MITER.
EDIT: If you want your 17 to look more like an issued rifle (as per SOCOM), this is what you'd want to replace the factory muzzle brake with:
http://www.midwayusa.com/product/873121/advanced-armament-co-aac-blackout-flash-hider-51-tooth-miter-suppressor-mount-762mm-ar-10-lr-308-scar-h-5-8-24-thread-steel-matte