According to my friend the best melee weapon is a crowbar, because it can do good damage, is practical in many situations (clearing debris, opening trunks, etc), lasts longer than other weapons (wooden bat, Katana, etc) and easy to maintain (simple grind polish would keep it usable).
Also, you need to be quite strong to cut someones head off with any blade, so as much as I'd like to use a sword, it probably wouldn't be practical (unless you weigh 200 pounds in muscle). I'd do well with an iron pole or pipe. I'm not strong enough to decapitate anyone, but I probably could deal a lethal amount of damage to a zombies head
