Not on boat trailers but I have owned 3 snowmobile trailers with torsion axles. 2 were fairly light and may be applicable for comparison to a boat trailer. My 2 place clamshell and a 2 place inline, dual ramp door trailer, probably 1500lbs empty. The torsion axles rode very well, a little bouncy when empty, but pretty nice. I recently bought my dream snowmobile trailer and was talked into spring axles by the dealership. This was a trailer I had built custom, no expense spared, and the dealer could care less which one I went with. They convinced me to buy spring axles. One major disadvantage of torsion is when it fails (and they all do at some point), it's usually a made to order item. Spring axle trailers can basically be rebuilt from parts off the shelf at a Tractor Supply store. Torsion axles have a zillion configurations- drop angle, knuckle length, axle width, mounting tab size and width... so if you are on a trip and something happens (Murphys Law), it's a lot easier to deal with leaf spring axles. To be fair that is something much more applicable with a snowmobile trailer than a boat trailer, at least for me. I often times pull my sled trailer hundreds of miles away from home for a week, but the boat not as much.
As far as the ride quality, I was convinced that I would be sacrificing that by not buying torsion axles, but it seems I was completely backwards in my thinking. The leaf springs ride far better than my torsion axle trailers since they aren't as bouncy. So while I was once a firm believer of torsion axles being better, I have been shown the light. Keep in mind that most torsion axles are linked side to side, so when one wheel hits a big bump they both react to it. Leaf springs are much more independent suspension.