If it had truly come down to being allowed only one rifle, then I assume something else has gone wrong as well.
So, an AR 15 would probably be useful.
If we are talking just normal hunting scenarios, I would consider 30-06, 338, or 375 in a solid bolt action. For me, it would be the 30-06. Most likely in a Winchester or Ruger.
It's hard to not pick a 30-06 for an "all arounder". It can do damn near anything. Not real classy, not real fast, not a lot of cool factor, but it damn sure gets the job done with boring regularity.
