Whether torsion or leaf is better is a matter of opinion. The torsion is a more independently articulating suspension. Is that better on a trailer? Is it worth the extra money? You have to decide that for yourself.
YouTube has videos from Dexter explaining how the torsion is built and why they believe it is better. Keep in mind, anything can be made to look better for sales.
My opinion is, I want leaf springs. Tried and true, easy to repair or replace, and easy to understand.
Regarding spacing of axles, greater spacing helps balance the load across the axles, which basically means it is more forgiving of how the trailer is loaded, and possibly less apt to sway if loading is less than ideal. The downside as you surmised is added scrubing of tires in a turn, added side load on axle hangers. Like most things, it is a compromise.