A baseball bat or a Ax.
i think you are gonna need a weapon that you can swing around for a long time and in a crowded area so you dont get tired or overwhelmed. I would use an oar or a machete. http://zombietools.net/tools/ here is a website with some good ideas for what to use. (no i'm not trying to advertise)
I have a variety of melee weapons many of which can be viewed here.
There is a lot of discussions like this one on the site and I find all of them a fun and entertaining concept to consider.
There are a lot of factors that should be taken into consideration when choosing a melee weapon. A melee weapon will be (or should be) used in offense only when silence is required or as a weapon of last resort. That in mind, I will share some of my experimentation and resulting observations.
Bladed weapons (most often the Katana amongst those who wish to feign the type of badassery that will likely get them killed) have certain unalienable definciencies that cannot be avoided except by the most skilled of combatants. Since, as a general rule, weapons must follow the "Get the head you know it's dead" principle, that means that your bladed weapon must either pierce the cranial cavity in order to do mortal damage to the brain or you must remove the head from the body usually by decapitation. While decapitation is fun for games and books, it is exceptionally difficult to complete with any bladed weapon by someone who is not an expert swordsman. Decapitation is by skill or dumb luck and sometimes both. Bladed weapons of any sufficient length to make them useful in single combat with a zombie will be cumbersome and at times heavy (depending on type). Another drawback is that the blade, if unable to complete travel through the skull, can become wedged in causing you to lose your melee weapon or make it too cumbersome to weild any longer.
Polearms present another variety of weapon that can be used against the undead though rarely to effect casualties. Instead, polearms are more effective in single combat when you are trying to keep the ghoul away from you, perhaps long enough to use the other weapon (a sidearm perhaps?) that you should likely have been using in the first place. Polearms are even more cumbersome and heavier than their shorter bladed counterparts and even a person skilled in their use against multiple human opponents will likely find themself foundering against a mass of the undead.
Clubs (in my opinion) present the best of the melee weapon category for a variety of reasons but also, like any weapon, have their own drawbacks. For clubs I would suggest anything with angular surfaces that will focus energy into a point or ridge that can crush or shatter bone. The cranial cavity, even at the temple, is well protected from concussion so weapons that provide an opportunity for a massive crshing blow are the best. For this I would suggest Maces (not the type you spray from a can) or Native American style war clubs (such as these or even these). The drawback to the second style is that the weapon reaches maximum efficiency when wielded from a single direction of travel (i.e. when the ball end is forward to the target) which limits its functionality. The drawback to such weapons are the likelihood that splatter will result which could just as easily ruin your day...
Tomahawks and small axes such as these are lighter in weight and functional in more than one manner making good tools outside the realm of zombie busting. SOG also makes a line of excellent "Tactical Tomahawks". I own three myself.
I just seen SOG Tactical Tomahawks, well that right that wrote my response to the topic. In the market for one but keep getting sidetracked by other things.
Are the SOG tomahawks weighted at the top?