if i would use a firearm from anny universe i'd use iridium weapons from borderlands 2, something in the range of a SMG or assault rifle. but if where talking real life guns, i'd go with a coilgun, it's fairly lightweight, simple ammo which you can manufactor yourself, with the olny backdraw of using batteries, tho a small raid on a supermarket would fix both your ammo and battery issues :P
'Something's awry.' -Duhgan 'Bel' beltayn
'A Man choses, a Slave obeys.' -Andrew Rayn
Clearly a spud gun is the superior Zombie killing weapon.
No one mentioned this yet... really surprised thought the thread would be full of them... hashtag first!
Skip to about 1:00 for the good part. I'd like to see any zombies (or...well, really just about anything) try fucking with me if I had one of those.
edit: woops, just read the OP again... "from any game"
In that case I would go with the BFG-9000 from Doom.
I'l take the tesla trooper suit from C&C red alert.
Id take the krysae sniper rifle from me3 before they nerfed it.
"The Krysae's scope uses a rangefinder that adjusts to keep the target in proper proportion to the shooter, which comes in useful when the sniper is forced into close range. Its specialized ammunition is both armor-piercing and explosive." Its a sniper rifle that shoots explosives!
You would be able to sit on top of a building and just shoot zombies and kill the others from the splash dmg. More would come to the site of the explosion because of the sound and be turned into zombie juice. With infinite ammo you could probably clear a major city in a couple weeks.