Fiberglass is lighter, easier to repair, results in finer lines, but is more expensive. Fiberglass is generally more rigid than plastic, which can result in a faster boat. Fabric is labor intensive to build though a little less so than wood, fragile, and needs maintenance. They are generally more expensive to buy than any other kind of boat, but there are other considerations that may make them a better overall value. See section 5, folding kayaks, for more information.
Inflatable boats tend to be much less expensive than any other sort of boat.
Rigid boats may perform better than folding or inflatable boats. Folding and inflatable boats have the advantage of easier portability and storage. If you plan to travel with your boat, a folding or inflatable boat will be easier to get on airliners. You can pad any boat, but it should fit you fairly well to begin with. Some boats fit big people better, some are better for small folks.