Lets see, video game zombies, check. Movie zombies, check. Real life zombies?? The only shamble????
Anyway, everyone should know that zombies are slower as they decay and age. I'd like to prepare for the faster ones and use the shotgun. As mentioned, the rifle is really only useful for those few people who would be able to aim the damn thing. Just about the only thing that's been said that is a good point is the ammo size. Rifle ammo is more compact, but if you're using more of it due to poor aim, you're not doing yourself a favor.
I keep reading 'you shouldnt let them get close enough to need a shotgun.' Try going through an entire day without letting one human being within 10 feet of you, especially if you live in the city. Almost impossible, no imagine all of them just wandering around aimlessly until they smell your fresh braaaaainnnzzzzzzz....
Debate it to death, but the shotgun (especially this AA12 model for automatic, low upkeep, near zero recoil, and clip loading) is perfect for the zombie invasion.