Sniper Rifle - You’re holed up in your fortified position (hopefully not the basement, dude, have you watched a zombie movie?) and you need to thin the herd. They already know you’re there, you just need to kill as many Zombies as possible while putting yourself at no risk. Enter the Sniper Rifle. Easy to use (relative to later weapons), crazy-accurate and most importantly you can eliminate as many shambling horrors as bullets can provide.
Thats gonna leave a mark!!