I'm my wonderful experience of searching out the perfect trailer, I am starting to get hung up on axles. Nothing seems to be made in the US anymore and the quality of components can be questioned. Lets say most things are equal and compare the types of axles.
Here is the little I know about these types of suspension. Lets try to expand and get more info.
Slipper Springs - Seems to be on every trailer I look at that is 12K or 14K. Every trailer sales guy says they are the best, but reading, these springs seem to be the ones with the most complaints. In reading, they are crazy noisy, very harsh unloaded, and tow horrible. With that said, they seem to be the easiest to maintain and replace.
Shackle (eye) Springs - These seem to be popular on the smaller trailers. The complaints are that the bolts wear out in the shackles. Not many people talk about them.
Torsion - Some people think these are the best thing since sliced bread and others are haters. Most agree that they will last as long as they are not overloaded. You have to keep your trailer level when towing or you could overload an axle. The axles do not share the weight. The best unloaded and loaded ride out of all of them. BUT, you have to replace the whole axle when they wear out. They are also the most expensive.
The upper end trailer I am looking at is a torsion system. I am unsure if thats what I want or not....
Lets try to get as much info on these types of suspensions here that we can.