In reality shotguns arnt great for fighting off a zombie horde. Yes their powerfull and can even take limbs off but their also grossly inacurate and a headshot is reletivly unlikly. Its made even more unlikely by the fact that to use shotguns effectively you need to be fairly close to your target, if your target is a walking corpse moaning at you can wanting to take a nice bite out of your forearm your shooting is going to become very panicd and eratic.
The best combo would likley to me a M1 Garand, Colt 45 and a machete.
Why? Because...
1. The M1 Garand is accurate, powerful and fairly easy to use
2.The Colt, though inaccurate can be a great backup weapon and is fairly realiable.
3.The machete is light, easy to handle and has more uses than putting down the undead.
And always remember- Blades dont need reloading
Sol