Well at least we're only talking about shooting zombies this time, not focused on shooting people, although it does make a cameo appearance in your desire to have a back-up handgun. Keep in mind, that not all states allow concealed carry of a handgun while hunting, and other states may not allow open OR concealed carry of a handgun that isn't legal for the game you're after. My personal preference would NOT be an AR-10 for zombies, as the excessive recoil of the .308win in a semiauto platform quickly begins to waste valuable ammo, and 308win ammo is considerably heavier than 5.56Nato ammo, so you can't carry as many loaded 30rnd mags for the same weight in 308 as you can 556.
An AR-10 is not the same thing as an AR15. That DPMS LR-308 won't be very easy to "change around," contrary to what you might think based on internet tales about infinitely customizable AR-15's. The 308 length AR-10 versions out there are almost all independent, with very little interchangeability for parts other than cosmetics.
And as Tundra pointed out, not all states allow the use of semiautomatic rifles for hunting, and you should note, as much as you move around, that different states may not even allow ownership of a "modern sporting rifle" like the AR-10/LR-308.
The Rem 700 in .30-06 would be my pick off of that list.
BUT...
Comparing prices, since you have the LR-308 on your list, which tends to run around $1200, then it makes the least sense. For $1200, you can swing both the Rem 700 and a Rem 870 12ga. Depending on which models of 700 and 870 you pick up, you might even have enough left over to get a decent muzzleloader too. All for the same price that you would have wasted on the LR-308/AR-10.