Zombies mode upgrades

One machine gives your weapon the pack a punch upgrade, while the other machine, with the armor, can upgrade the tier of your weapon.

What upgrade is better for the gun?

Both are good for your gun, but pack a punch is the bigger upgrade. It maxes out on the third tier. First upgrade is 5000 Z bucks or whatever they call it, then 15k, then the last is 30k. For the damage upgrade on the armor machine it's 500 green salvage, then 1000 green salvage, then 500 blue salvage, and finally maxes out at 1000 blue salvage. If you plan on having high round games, you need both maxed. I've put a lot of time in zombies for gun camos, and I usually go to about level 35 and stop. The zombies scale up with you, and it just becomes a drag killing them unless you use the wonder weapons.

Also keep in mind that Guns of Legendary quality can drop but obviously are rare unless you get the wonder weapon or the ray gun (both are legendary only).