Honestly. I know its a bad idea, but my weapon of choice would be a .357
My uncle and I go hunting or shooting when im down in Texas visiting and I feel that its the perfect zombie hunting caliber. We use a .306 for deer and .357s for boars.
The weapon is small enough to keep you mobile and more than powerful enough to take out a boar, or a zombie, in one hit. And the revolver matches my hat and duster really well.
The only problem tho, what if there are more than 6 zombies, ok then I have two, but what if there more than 12 zombies?