For the funnest weapon to kill Zombies with, I think a lot of people in this thread already mentioned most of the things I'd use.
For the most practical, most people have it dead wrong!
First off, AA12s and other auto shotguns with huge magazines may be fun, and powerful, but they are overkill for a zombie and that overkill comes with
the price of added weight, lower ammunition carrying capability, more noise, recoil, and less comfort. 12ga shells are huge and heavy compared to many
smaller types of ammo. Which means the number you can carry will be far far less than with anything else.
Blades and swords are a great backup weapon, but as a main zombie killing weapon it's a horrible idea. First of all you have to be close to them,
which is a bad idea. Second of all, you need space to use them. Third, they take a lot of energy to use, which is not good if food is scarce and
quality sleep is hard to get. And last, unless you are the most skilled swordsman on the planet, odds are you are going to get eaten real quick if you
are trying to fight your way through more than a few zombies at a time. I personally feel there is no replacement for a good firearm in this type of
situation.
Now, we have to figure out what type of zombies we are dealing with here. Three main types being the slow stupid zombies that need a headshot to kill,
fast zombies that also need a headshot to kill, and fast zombies that can be killed by whatever would kill a regular human (such as in 28 days
later)
For the first two, I would choose a .22, either a Ruger 10/22 or Remington 587. They are small, light, semi-automatic, accurate, 30rd magazines are
available, and ammo is extremely light, small, and easy to "find" In addition to that, recoil is almost non existent, which means very quick follow
up shots if you are dealing with more than one zombie or miss with the first shot. Power isn't a huge issue, as the only way to kill them is to
damage the brain, so a .50 and a .22 will kill a zombie just as dead. And if you get a suppressed .22 it will be the quietest gun anyone will have.
At longer ranges a .22 will have trouble penetrating a skull, but if they are far enough away a .22 wont get through the skull, they are far enough
away to not have to deal with them. In addition to zombie killin' a .22 is a great round for hunting small game to feed yourself.
Now, if they are the 3rd type of zombie mentioned, I'd go with my trusty AK. Powerful round that will take down a zombie with ease, high magazine
capacity, semi-automatic, ammo that is easy to find, and can be used to take down larger game for feeding yourself. An Ak or other similar rifle might
be a better idea for all situations, considering odds are you will have to fight off other armed humans, not just zombies, in which case a .22
wouldn't be the best idea.
I probably just took all the fun out of this thread, so to inject a bit back in I'll say I'd use a Forklift as a weapon.