Bayou, as RAB says, it all depends.
In my experience the lighter the boat the less robust is will be. It is not that Carbon (or Kevlar etc) are not very strong materials, but that these materials are only used to get the boats weight down without compromising too much on strength.
But in most circumstances a fibreglass boat will probably prove to be stronger - but naturally heavier.
If your one of these people who does not regularly paddle in surf bigger than 4'; don't paddle over rocks, or into floating logs, or floating navigation lights; don't collide with other skis, surfboards, or power boats; don't tie your ski down too hard; or too loose; or drive about having forgot to tie it down at all; or drive into an underground car-park with the ski still on top of your SUV; or reverse into a telegraph pole, picket fence, house, bus, truck or other object harder than your ski; or leave your ski in the hot sun everyday, particularly with the bung still in; etc - then your ski will last a long time regardless of what it's made from.
But if your like the rest of us... resign yourself to the reality that you will have to repair that ski from time to time, or maybe even take it to the trash tip when the repair shop guys roll about laughing saying things like "...you want me to do what?".