.22lr. It can defend you in a pinch, get you food, and try carrying 2000 rounds of any other ammo as easily.
How about .22 magnum? You can get it in a lever, bolt, or a semi-auto. You can still carry a lot of rounds and the power level is quite a bit greater.
Yes, for the long run you need ammo more than firepower. But, as I've mentioned in similar threads, if you must defend yourself 22lr has insufficient range.
I don't think 5.56 is really that great of a round for hunting, though I have no experience with it. I would think even a 9mm would provide a more assured kill on a deer.
I would choose the M6 Scout. It's a two barrel single shot that shoots 22's & .410's