Call of Duty: Modern Warfare 3's Zombies mode puts a slight twist on the mechanics you are already familiar with. It now plays much more like a souped-up DMZ mode rather than its old round-based format. And Field Upgrades have been modified in terms of both their effects and how you get them just for this game type. There are six different Field Upgrades you can bring into the map and use on a cooldown timer to help improve your chances of survival, but you can only pick one at a time. You will begin the game with only one option, but steadily unlock the rest as you level up. Once you have them all, the question then becomes which is the best Field Upgrade? We've managed to exfiltrate with the answer.
Healing Aura
Regardless of whether or not you're playing with a team or running solo, Healing Aura is no doubt the best Field Upgrade to bring on any Zombie run. When activated, you and any teammates in the area will not only gain immediate healing, but it will also instantly revive any downed teammates. The downside to all this power is that this upgrade has the slowest recharge time and is unlocked at level 19.
Aether Shroud
This is another upgrade that you will be glad to have. Aether Shroud makes you you temporary invisibile to all Zombies. This won't make you invincible, mind you, and PMCs can still take shots, but if you're getting swarmed and have no way to escape, becoming instantly invisible to a bloodthirsty pack of zombies can save your skin more often than you think. This upgrade has a medium recharge rate and is unlocked when you hit level 39.
Frenzied Guard
Just past the halfway mark, Frenzied Guard has a massive upside, but not without some risk. When you pop this Field Upgrade, you instantly repair all your armor, but also draw all the aggression of any enemy nearby for 10 seconds. However, another perk is that anything you kill during this time also repairs your armor, so situationally, it can be great or detrimental. This one recharges slowly, unlocking at level 9.
Frost Blast
Frost Blast does exactly what you expect: it fires a freezing blast that will slow down any enemy you hit with it and deal a bit of damage. It's decent in a pinch, but not a game-changer. You can get it when you hit level 29.
Tesla Storm
An odd ability on paper, Tesla Storm is only good if you have a team working together. Activating it will create a lightning chain between you and your team that will damage and stun enemies that get close to any one of you. It lasts for 10 seconds and can be great in the final moments while holding out for an extraction, but not in other situations. It recharges slowly and is the last upgrade you unlock at level 50.
Energy Mine
This is your default Field Upgrade, so it makes sense that it's the "worst" on the list. Energy Mine isn't exactly bad; you simply lay down a mine that does what a mine does -- explodes. It's just that setting up traps like this in Zombies isn't all that applicable except when kiting a boss around or waiting for the helicopter. It has a medium recharge speed.