Like you my first grab is my M1A. .308 rounds will take just about anything I am going to encounter in North America. Squirrels, sorry but I have not problem blowing the little punks and going for the head if all I have ia my M1A. Then again if there is a deer, coyote, mountain lion, bear or even a seal .308 185gr is about all it is going to take.
Certainly a great weapon...but actually, I'd opt for the weaker .30 carbine. It doesn't have the wallop of a .308, but I can pack 1,000 rounds into just a little more than two shoeboxes of space. It's generally adequate for 2-legged vermin out to 150-200m and will take rabbit to deer size game without turning the meat into red fog.
If I lived in a more northerly clime, I'd probably opt for something more along the lines of your first pick.