The important thing to remember when choosing a Level III bulletproof vest or body armor of any type is that higher levels of them don't necessarily mean that they will work for everything below the ammo they promise protection against. Bullet proof armor is not always stab-proof, for instance. And bullet proof vests of level 4 can't protect against all of what level 2 keeps you safe from. Sometimes, the slow speed or distance make the shot a lower level, but allow it to get through the armor made for higher level attacks. Keep this in mind and choose a level of body armor with realistic expectations of what it will be up against.
Body armor comes in two types. You can get vests in the form of soft armor or hard plates. Soft armor refers to a Kevlar, Twaron, Dyneema (etc) woven material designed to prevent penetration of bullets through the particular weave it's made in. These are the more convenient type of bulletproof armor to wear, as they are less bulky and hot. However, they are typically made for the lower levels. If you need anything lower than level 3, soft is the way to go. It also makes a wonderful layer of protection for under plates, as some types of plates require (some plates are standalone and require no under layer, and those are called STA, but some are made to be worn over another layer of protection, and those are called ICW, for 'in conjunction with'). Hard armor plates, on the other hand, are made of ceramic or polyethylene, and are less convenient, but are capable of stopping more powerful attacks. Ceramic is made to break, scattering the impact of the shot, where polyethylene does not scatter the impact, but prevents it from penetrating. They each have pros and cons, and you can choose accordingly. Ceramic is not made to withstand many shots, but scatters the impact better, and wearing polyethylene, you absorb the full impact of the shot (which can cause injury on its own but is not generally lethal), but it can protect against more shots, as many as it has space for.
Level 3 or so is the most commonly purchased level of bulletproof vest, as it is capable of protecting the wearer against most of the more common threats. They are within the category of rifle plates, and they can protect against six spaced hits of 7.62X51MM NATO (Full Metal Jacket) travelling at 2,750 feet per second, or a .308 Winchester hunting round.
