The most important thing to keep in mind when picking out a weight distribution system is the weight of the load you'll be towing. Weight distribution systems are rated in two ways: the gross trailer weight they can haul, and the tongue weight they can distribute. You want to make sure both of those ratings are above the amount you're looking to tow -- but not too far above it.
For example, if the weight distribution system has a 1,000 pound (454 kilogram) tongue weight capacity but the trailer is loaded with only 300 pounds (136 kilograms) of tongue weight with 50 pounds (23 kilograms) of cargo in the trunk of the towing vehicle, you're about 650 pounds (295 kilograms) under the rating. That can make the distribution unpredictable and dangerous. On the other hand, if the system is rated to 1,000 pounds (454 kilograms) of tongue weight but you're attempting to distribute 1,500 pounds (680 kilograms) of tongue weight, the system won't be able to distribute the weight effectively and you'll also have some serious problems. Keep that infamous rule from "The Price Is Right" in mind when choosing a weight distribution system -- you want to bid the closest without going over.
A second choice you'll have to make during the selection process is which type of spring bars you want in the system. There are two common basic styles: round or trunnion. Round bars usually offer a little more clearance space for hooking up the trailer, but trunnion bars can increase the system's weight rating. The advantages presented by either round or trunnion bars vary from setup to setup, so it's good to consult with someone who has experience while you're trying to decide.
Another factor to consider when purchasing a weight distribution system is whether you want additional features like sway control. Generally, the systems are naturally less inclined to sway so you can probably hold off on that purchase at first. If you're still experiencing sway (and provided you didn't do a really bad job packing or are driving too fast), then you might want to look into adding a sway control system too. Some systems are two-in-one, with weight distribution systems and sway control systems combined.
On the next page, we'll look at how weight distribution systems are installed and the nitty-gritty on how they operate.