12 gauge. Most versatile, you can take pretty much any legal game in North America with it, provided you have the proper load. In a gas operated semi auto such as a Remington 1100/11-89 or Mossberg 9200 the recoil is less than a .410 or .30-30 rifle.
12 gauge shells are available world wide, even in the smallest and remote of hamlets, and is cheap.
Gun Control is a MUST! If you cannot control your gun get one you CAN!