"-I don't know about your area but in mine .40 S&W is quickly becoming the choice of law enforcement followed closely by .45 ACP.

-There is no such thing as the ultimate zombie killer..........Yet."

"true, but with an M1A i can dispatch the enemy from hundreds of yards! silence can be traded for distance and effectivness!

.308 vs 9mm, zombie or raider, u can truly reach out and touch someone with an M1A"

"only a couple cons with this weapon (it is nice):
1) it fires 9mm which if you needed to shoot a raider is not very effective
2) its a spray and pray weapon mostly
i would stick with something a little more powerful such as a UMP in .45 "

"Not really. The "ultimate zombie killer" weapon is something that best fits a user's needs. That is, it must be effective, efficient, and easy to use or well trained to the user. Sort of like a simple Colt .45 in a trained veteran's hands can prove to be more valuable than a squad machine gun in the hands of someone who doesn't know what they're doing.

Also that's kind of why humans aren't restricted to only one weapon... Heh heh heh

@the idea of an MP5SD being a great zombie killer. Not a bad weapon (accurate, silent, light, easy to use, reliable under most circumstances, 9mm ammo is very plentiful and cheap, and low recoil). But it does have its cons, like many already have stated: 9mm has very little stopping power, if any, so it will be annoying to the shooter if s/he has to constantly reload after having downed only half a dozen or so zombies with each 30-round magazine.

A UMP .45 would solve the problem of stopping power but trade capacity for it. UMP .40 would also work fine.

Good weapons would be reliable, light, easy to use, accurate to a distance, maintenance-free (mostly), able to be suppressed, have good stopping/killing power, durable, and use ammo that is cheap or plentiful.
Examples: UMP .45, AKS-74U, AK-74M, AKM, SCAR-H, FN FAL Paratrooper, G3KA4"