This is a common question and the subject of much debate among zombie preppers. The truth is there is no one best weapon for anything; that's why so many weapons exist in the world today. A number of factors come into play when choosing a weapon. This includes availability, training and situation. While American preppers tend to lean heavily toward firearms, this isn't a practical option for people who reside in countries where such weapons are not widely available. As we saw in Simon Peg's film “Shaun of the Dead,” the protagonists knew of only one gun and they weren't even sure if it was functional. Historically, people have made use of a variety of tools and farm implements as weapons for the very reason that they were what was at hand. The same is true of a zombie outbreak. You might find that if the apocalypse happens while you are at a wedding reception, the best weapon is a cake knife and a broken champagne bottle for the sole reason that they were the only things available. Next is the matter of training. If you've been playing baseball since little league with a batting average of .475 and 20 homeruns, a bat would be a better option than a katana, regardless of you've seen in the movies. Most weapons require training to be used effectively and some, like the katana, are probably more dangerous to use if you haven't had the training. Finally, the situation can dictate what you need. If the zombie is 100 feet away, and you've got a knife and rifle, the choice is obvious. But in close quarters or at a time when stealth is required, the reverse is true. All that being said, in my professional opinion, my ideal combination is a lightweight rifle (preferably .22 caliber) and a hand ax. The .22 rifle is reliable and accurate with lightweight and plentiful ammunition. The ax is durable and serves a multitude of functional purposes as well.