Since I am a huge fan of zombies and firearms I have thought of this countless times.
First of all, the Zombie Survival Guide suggestions are not very educated, as the man seems to have never heard of modern assault rifles (come on, an M1 Carbine? Good luck finding ammo and mags in a pinch. You'd be better off using a .22 and gambling head penetration with the punier, more common round.) If you're picking a gun, you aren't just picking what gun you'd like to shoot. The gun has to be able to adapt to the environment, and there are few that can actually do that.
For a sidearm, 1911s are good. They will last and are good shooters generally, and you can find a helluva lot of magazines for 'em wherever you go. This also goes for my other choiced, Glocks (lighter, hypercapacity pistols) or Berettas (Military issue, so if you stumble upon dead soldiers, chances are they have ammo for ya). A small .38 is also good for use as a last resort, be it for the zombies or yourself. There's little that can be done to a revolver to make it stop working, so if you plan on using it, on whoever, it will work.
Which brings me to my rifle choice. Yes, rifle. I might have a sawnoff shotgun for breaching or absolute last resort (with the stock still on, mind you, aiming from the hip is nigh pointless when you need a headshot). I'd choose an AR-15 build gun, and I will tell you why. Normally I argue against 5.56/.223 Rem and it's chambering in the AR-15 as it has less energy than my champ, the AK 47, but it has what has always had, accuracy. Zombies only go down with headshots, so additional stopping power doesn't matter. What does matter is precision, as well as penetration at distance, not that you'll be sniping or anything, but 5.56/.223 will do this at insane ranges. Not only that, but everyone and their grandma has an AR-15, so ammo and mags are everywhere for you to take and use, and since it's lighter than other rifle rounds, you can carry a lot more ammo. In short, it's a good balance considering all the bonuses and all of the negative things that become null and void.
Also, full auto is not intended for zombies, but potential renegade groups that may try to kill you for your stuff, as seen in the first Dawn of the Dead. Other than that, keep your selector on semi.
Also, I did a thread on my forum about this a while ago. While not strictly a gun forum, we do sometimes have good gun threads. Feel free to browse at any of the arguments presented there.
http://diseasedboard.proboards.com/i...ad=1261&page=2