We ran torsion axles on the old boat's trailer. It did ride nice, and never had a problem with them being torsion. It had other problems, caused mostly by the fact that it was a triple axle and generally a POS.
The new boat rides on a tandem axle trailer with leaf springs. It clanks and clunks if you drop it off a curb, as the equalizers do their thing. Other than that, it is great.
Boat trailers are convenient in that you level them once, and then they stay pretty much static.
My flatbed is a tandem axle with torsion axles, and behaves as mentioned earlier - bouncy when empty, will lift a tire on uneven ground. Being a 30 foot flatbed, you have to pay attention when you load it - getting it out of level is easy to do and not a good place to be. Once you get that figured out though, I've got no problem with the axles.
