Lets get down to business.
Infantry Vest
Equipment Slots: Tactical, Lethal, Field Upgrade.
Gear Slots: Gloves, Boots, Gear.

Standard issue mobile infantry vest.
Increases Tac Sprint duration and reduces refresh time.
Duplicate effects do not stack.

If equipped with Running Sneakers, you gain the effects of Lightweight Boots.
Enemies will also drop intel packs when they die which generate a radar ping when collected.
Gunner Vest
Atop our list, the Gunner Vest.
As mentioned, this vest grants you the ability to carry two primary weapons, enough said.
Wait, actually, theres more.
Unlocked at level 20, its most definitely worth it.
Thats everything on the best vest in Modern Warfare 3.