Fortunately, torsion axles and leaf spring axles are each well proven and durable.  Making a choice between the two is typically a matter of preference.
Leaf spring axles are well recognized; they use layers of steel springs (leaves) clamped together to provide suspension. Leaf spring axles are a more traditional and common type of axle.  A torsion axle conceals rubber cords to provide resistance to the suspension arm; the system is less noticeable.
General comparison:
In summary, a torsion axle offers a smoother ride and requires less maintenance but is more expensive and can be difficult to repair. A leaf spring axle, on the other hand, is more economical, easier to repair, and suitable for heavy loads, but may provide a rougher ride and require more maintenance. The choice depends on your specific needs, budget, and the typical loads and conditions the trailer will encounter.