My two picks would be the CZ858 and the Swiss Arms Classic Green/Black Special.
I ran my 858 in a two-day Hackathorn course last month...worked well, although the increased recoil over a 5.56 will slow you down a little bit.
The SIG rifles are one of the greatest fighting rifles ever built, to stupidly high QC standards.
On a budget, go 858. If you have money, go SIG.
I would skip the XCR for a lot of reasons, and the SL8 is an accurate but bulky, heavy gun best suited to precision fire, so that would heavily influence my decision on that machine.
M14s are fun and I built a fair number and played with them a lot, but they are expensive to feed and all the optics mounting solutions are kind of annoying IMO. If you want a .308 with irons, they are a good choice.