I would say a heavy barreled Remington 700 in .308, but I'm partial to the brand and the caliber. I would pick the Remington because it is a fine all around rifle and capable of very good accuracy. I would pick .308 because of the easy availability of both commercial loads AND 7.62x51mm NATO loads, and there are reams and reams of loading data available for the .308 if you want to load your own. And, in a heavy barreled rifle of almost any brand, .308 will shoot well to 1,000 yards depending on your load selection. Also, .308 will go through 5 or 6 zombies, depending on their level of putrefaction and your bullet design.
In my family, we own one each of Remington, Savage, and Ruger rifles in .308. They are ALL good, serviceable, and accurate rifles. Both the Remington and Savage have heavy barrels and routinely shoot at .5 MOA or better. The Ruger is a light barreled sporter, and shoots about 1-1.5 MOA. The Remington has a nicer quality of build than the other two and functions more smoothly than the other two, but the Savage is more rugged than the Remington. Both the Remington and the Savage are very effective long range rifles. The Remington and Savage have better triggers than the Ruger. The Ruger has controlled feed, which neither the Remington or the Savage have. The Ruger would be better as a reliable short to mid range rifle (because of the controlled feed) during a zombie invasion. The Remington and Savage would both be better as stand off weapons, where controlled feeding is less of an issue during a zombie invasion. Think of the Ruger as a battle rifle with a bolt, and the Remington and Savage rifles as artillery.
Personally, if I had to divest myself of all but two of my weapons and was faced with a zombie horde, I would choose the Remington, and either my .44 Magnum Model 29 OR one of my 1911s in .45 ACP. If there was no zombie horde, but a comet hit the earth and ended civilization as we know it, I would pick the .44 revolver and an accurate bolt or single shot rifle in .22 Long Rifle.
Does that help?