You know, if I had to have only one, or grab only one if I had to bug out RFN, it sure might be the AR-15. I like how light it is, and how I can carry more ammo for less weight with it than high powered rifles. I can hit just about as well with it as I can with the .308 AR out to 400 yards or so... better at the closer ranges. If I had to use it to get game, it will kill anything in my part of the country no problem. Yep, if I had to grab only one, it would definitely be the AR-15.
Thankfully, due to double rifle cases, I shouldn't ever have to make those kinds of choices!