I'm definitely no expert on these types of guns but:
My first, about two years ago was a gift from my mom-in-law. At the time, I just said maybe a .308 as I was thinking hunting deer/plinking combo gun. I received a Rock River LAR 8 with a EOTech holographic sight. I wasn't able to pick it out but smiled
a lot anyway. I probably wouldn't have spent that kind of money but wasn't going to say "No thank you". Trouble is the gun is HEAVY and not the easiest to carry in the woods, even with a sling.
My second, I bought myself. A Stag Arms 5.56 gas piston carbine type with flip up iron sights. Love it. The .308 stays home most days if hunting deer and still carry my trusty Marlin .35 lever gun. 20 year old military surplus ammo for horsing around is cheap for both, especially tracers, especially if bought in quantity. Just have to be careful if it is dry. Don't want to start a woods fire. I've never done this and may be an old wives tail but don't want to risk it.
No more than I shoot, the gas piston is probably over rated. I'm looking for a .22 conversion now for the 5.56 and found out I'll have to take the piston out for it to work.