For survival, you can take deer even if all you have is a .22 LR.... however this is clearly not the ideal round for the job! Along those lines, 5.56mm will certainly do the job. Again, generally frowned upon for recreational hunting, but when you're in a pinch like a survival situation, you use what you have. As mentioned though, small game is what you'll probably be nibbling off of mostly...

What you chose largely depends on what it's for. An M-6 Survival Rifle (.22 LR or .22 Hornet over .410) would be great if all you were using it for was hunting small to medium (deer) sized game. It might found a little lacking if you come across a bear, or an armed enemy of the two legged variety though!

You didn't mention expense, but a good milsurp bolt action (enfield, mosin nagant, etc) or an SKS, if you perfer semi automatic, are a couple of very reliable, very ruggid options that won't break the bank.

It all comes down to what you'll be using it for, and what floats your boat- some people like the full power rifles, some like intermediate powered rifles, some like lever actions, some like bolt actions, some demand something in semi auto... so on and so forth. If you really like the combo guns, and if the M-6 is on the smallish side for your tastes, there are companies that make combos in larger calibers. Savage, for instance, offers a combo gun with a 12 gauge on bottom, and a variety of rifle choices on top: http://www.savagearms.com/24f12.htm but it's expensive