I usually don't get involved in this topic, but I have to say, Guns, Screwdrivers and chainsaws are all wrong. For quite a few reasons, but mainly sound and renewable use. for guns, they are loud and with the main industrial system not running, ammo would soon be a scarce commodity, that also goes with fuel for chainsaws. And yes, I know you can make gun powder and melt lead and make primers. but do you personally know how to do that? also with screw drivers. too up close a personal. it is also extremely hard to puncture a skull, in no way is it like that of puncturing a water melon :P.
So, if I had a say in the ideal zombie killing weapon. I'd say a splitting axe. For a few reasons. One, they are multi-purpose, you can split wood for a fire and use it to get out of rooms even without a key to a locked door. Two, They are not so heavy that they would slow you down too much, although it depends on the axe, most splitting axes are quite manageable. Three, They are easy to look after, axe sharpening kits are fairly inexpensive and small enough to take with you on the move. Four, unlike a screwdriver, they have enough swinging range so that you can keep out of arms reach. Five, due to the nature of a splitting axe, they have a lot of momentum and can split through skulls easily.
So, TL;DR:
A splitting axe is ideal, everyone should have one. I personally have quite a lot, in all variates ranging from Carving axes, felling axes, splitting axes and throwing axes.
Now, I'm gonna go back to being sane.... /*Looks at everyone with wild eyes as like that of a trapped FISH in a net...*/