Those are both good choices Kach and Corise.
It would depend largely on the situation for me. The problem with .22lr and .410 is the same for both; stopping power. If I were, say, among the last survivors of some cataclysmic event (see: plague/sickness etc) and wouldn't need to worry about blasting hoards of zombies or otherwise possessed individuals I would totally go with an M6 Scout - easy ammo to find, and powerful enough to take down any game you might want to feast on without being wasteful and taking down large prey (see: deer etc) plus it's a rugged little gun, light weight, and super reliable. In that situation, however, I would want a back up... probably a pistol of some sort and if I had my choice, given the ease of use, I would take a larger caliber pistol to keep handy on the off chance that I became the prey for a large predator (see: bear, cougar, etc) and needed to act fast, make a lot of noise, and scare the beasty off. To that end I would probably use a .357 Remington. 9mm ammo is easy to come by in most parts of North America but as any police officer will tell you it comes up short for put-down-punch in a pinch and instead relies on rate of fire.
Now, if we're talking strictly about the Zombie Apocalypse I would want something large caliber with a high rate of fire, ease of use and reliability...
I know it's cliche, but in that situation I would probably opt for the ubiquitous blaster, the AK-47. It has demonstrated reliability - drop it in a lake, run it over with a truck, and it will still pop off rounds and should you come across a jam or misfire it's a remarkably easy firearm (see: long arm) to clear. Second only to .22lr is 7.62 ammo, which has been mass produced since forever. It has good range and decent accuracy and with selective fire, should you find yourself being closed on by a hoard of hungry undead you can pretty much count on me dropping it to hip fire and letting loose.
But even Zombieland shows, as Tallahassee demonstrated time and again, it depends entirely on the type of zombie you're dealing with in which case just about anything can become a weapon.
Don't forget your cardio.
