I agree. The pump shotgun is hard to beat. Funny thing though. I've got 3000 steel cased and brass cased rounds through my AR 15 and haven't had one stoppage, FTF or FTE. That includes running through 2 local training courses. That amount of rounds has been set through the carbine since December 2010. I guess it all depends on what ya got. Now, I doubt I'll go through the entire lifetime of my AR without a jam but it is what it is.
Any gun can have a malfuntion. Pump shotguns can bind up but are less likely to do so. Anything with moving parts can jam.
If you've got a weapon maintain it according to the manufacturer instructions.
Chainsaws are too loud and bulky for survival purposes, but if you were done, trapped, bitten, finished, it would make a good weapon for messing some zombies up. My advice would be to have one if you trek off into the wilderness, if your mode of transport can carry it. A shotgun would be useful- If you're worried about noise, check out the Red Jacket firearms silenced shotguns. As for rate of fire and reload time, a SPAS-15 (not SPAS-12) is a discontinued semi-auto shotgun still obtainable in Italy by private purchase. It uses eight-round detachable magazines. Even better is the Remington 870 Special Operations Weapon-mod, which is a fully automatic upgrade of the 870 with twenty-round quick change mags.
As for knives, I'd recommend having one or two on you anyway, a long, sturdy one and a smaller one tucked away.
My nomination for worst weapon would be the flamethrower: Its bulky, it kills by sucking the air out of you for the most part, it would take a while to destroy the brain. And until it does, the zombie becomes a (sorta)human torch