For whatever it's worth, I have had small (12 foot box!) single axle trailers for the past 17 years. My first one had a torsion suspension. It was not a smooth tow -- bouncy and noisy.
After six years, I got a new trailer (virtually identical to the old one) and had the dealership install leaf springs, shocks, and an axle flip (for better ground clearance).
Since then, I have towed about ten thousand miles a year, with no bounce. We tow on everything from rough California freeways to two-track forest roads.
I have an anti-friction sway bar -- the trailer is too small for a WD. I do pay careful attention to tongue weight, and I am running Endurance Load Range D tires -- which is way more tire than I really need.
But this is just anecdotal info -- I am NOT an expert.
I should also add that I use a "quiet hitch" type device to take the slop out of the connection between the ball mount and the receiver. It makes a big difference -- absolutely no "porpoising," lugging, or chugging.