I've seen a few discussions about torsion axles on the forum. I really don't have a strong opinion about them one way or the other. They are very popular in the teardrop trailer community. My trailer has springs, but I just built a frame for a friend who is using torsion axles.
In the offroad environment my concern would be with their strength. If you buy a beefy 2000 lb axle, then your trailer is oversprung for the weight that you are carrying. If you buy 1000 lb axles then you might be understrength. With a spring axle setup you can purchase a 2000 lb axle and use 1000 pound springs to achieve the desired strength and still have the appropriate spring rate for the load.
I don't think there is a "right" answer. Each of you will need to make the decision you are comfortable with and share you experiences with the rest of the community.
I do want to post a word of warning here. (and a few photos). A friend of mine used torsion axles on his beautiful teardrop and recently had a major issue. The most important fact is that his axles were machined so they could be greased externally using a grease gun. It appears that the machining caused the axle to be weaker than it should have been.
A few weeks ago a bunch of us met just outside of Austin Nevada for a weekend get-together. On the way home his trailer broke a spindle and ended up in the desert.
Again, I am not condemning torsion axles in general, but I would stay away from the ones that are machined for external lubrication!!