Things to remember ... a zombie can only be stopped if the brain is destroyed. Shrapnel weapons and explosives might be too chancy. Also, during the zombie apocalypse, killing 5 or 10 zombies with an AR might draw in hundreds or thousands more toward your position. These guns might be good if you are zombie hunting, or have a vehicle for quick escape, but you probably wouldn't want it for defending your stronghold.

A .22 handgun with a high capacity magazine and a suppressor (homemade if laws forbid them in your area) would a good choice for close up protection.

A carbine might be as much good too, maybe even better.

For stealth, a bow or crossbow would be ideal. But you better not bring one to fight dozens or more of the undead...