*Warning, silly topic debated seriously*
After watching many movies/playing video games/reading zombie survival literature, I'm convinced almost all the conventional thought regarding hand to hand zombie combat is pretty much wrong. This topic will not discuss the use of firearms/bows or medieval weaponry, as battle ready swords/maces/etc are hard to obtain in the modern world.
To me, there are only three weapons worth considering if one is "preparing" for the hordes of zombies. Of course, in any scenario if one is unarmed and a zombie approaching, they should use whatever is handy at the time to them. I will break the weapons down into one handed vs two handed to illustrate my point -
One handed weapons - I am convinced that only one weapon in this category would even be worth consideration. That weapon is a knife. And no, I am not talking for use on a regular basis vs zombies, but as a last ditch I'm about to be bitten and nothing is available, so pulling the knife out of the sheath and stabbing might just be the only answer. This flies in the face of most arguments I see, where machetes, tomahawks, crowbars (crowbars deserving their own section about why they make very poor choice), hammers, etc are suggested for use in zombie fighting. I submit these would all make very POOR choices to arm yourself with in preparation. There are several reasons I make this claim. First, most of the bladed weapons would tend to get stuck, and most people would not have the strength/know how to fight with them correctly (perhaps if they were to chop at the neck rather than head, then maybe, but in the heat of battle this would be easier said than done). The main reason I say none of these weapons would make a good choice is that other than not generating as much force as a two handed weapon, if a person using them made a hit but didn't kill a zombie, they don't provide enough force to knock a zombie down or at the very least, imbalance them enough to take another swing at the zombie.
I say crowbars deserve their own section on why they make such a poor, poor choice is the fact they are often touted as the best choice. I am convinced most have not handled a crowbar before coming to this conclusion. First off, crowbars are not nearly are ergonomic from a weight standpoint (their weight is distributed throughout the bar for the most part evenly, as opposed to something like a hammer where it is focused) as other weapons mentioned. This makes swings with the weapon more awkward and not as effective for the most part. Second, crowbars are very uncomfortable to grip, unlike other weapons mentioned where the manufacturer designs the tool with the grip in mind. True, wearing a glove or attaching a makeshift grip can alleviate this, but not to the point of easy a grip as say, a machete or hammer by any means. Of course crowbars can be used like a spear to stab, but in reality, I doubt this would be as effective for most folks as a swing.
Two handed weapons - These weapons should be the bread and butter of zombie combat if hand to hand combat is needed. Rarely does zombie related media focus on them, other than the baseball bat, as weapons survivors use. It's too bad, because they should be your focus. They offer more power than the typical one handed weapon in most people's hands and greater reach as well.
Of all the two handed weapons, I believe the best two choices would be either the axe (modern variety, not medieval viking axe or something, which remember I am not focusing on) or the sledgehammer. These two are often the most argued against using due to their heavy weight. First off, two handed axes are available from 4-6 lbs and sledgehammers can typically be bought from 6-8 lbs. The 20lb behemoths are obviously not very practical. At the lighter weights, most people of normal stature can swing with decent force for them to be pretty effective. Of course if 20 zombies are barreling down on you, they would not be effective, as they do take longer to ready to swing, but in reality no melee weapon would really save you at that point. But the good thing about these weapons is they were built for very high durability and very high destruction potential (they chop logs, demolish houses, break rocks, etc. Can a katana claim the same?) . And, even if they were not completely effective the first swing, they would most likely either knock a zombie down, or at least cause an imbalance long enough for the user to take another shot without getting bit. This is something that can't really be said for bats, shovels, spades, etc which just generally don't focus the weight enough at the head of the tool to provide the leverage to do so. The axe gets a slight better nod at one shot kills than the sledgehammer, but this pretty much evens out in my opinion due to the fact the sledgehammer will not get stuck in a zombie under most circumstances.
Two handed crowbars would be much, much more effective than the shorter variety, but I believe the same arguments against them would still remain.