I've had a H16, then a TheMightyHobie18 SX, a Nacra 6.0na, and finally an Nacra 20. I by far find the Nacra to be higher performing, more thrilling boat. The N20 is by far the most thrilling boat I have ever sailed. Neither my 16 nor my 18 went soft (I only had them for a few years), but the cams were a pain to replace in the rudders. The N20 seems a little more fragile than the 6.0, and def. more fragile than the 16 or 18, but I still run it very hard and the performance is worth it. Generally speaking, I have found that Hobies don't last as long (delaminate), but replacement parts are usually easier to find. What it comes down to, though, is don't buy a boat that you don't like (or is soft).
Trey
N20 314
Layline Rigging
www.velocitysailing.com