There are many great seats on the market, but in my opinion, nothing beats a custom carved seat for your body. They are easy to make, - 1-3 hours, and are always comfortable. All my customers are able to stay in their boats comfortably for 4-6 hours. They don't need to be adjustable since you won't be shifting around every 30 minutes to relieve pressure. They can be larger to distribute body weight better, and can be made to fit any boat. Carved from high desity foam, they don't absorb water, can be cut to within 1/4 in. of hull and still you wont feel the boat underneath you. Oh, and they are much warmer than some other fiberglass seats. As for cost, the foam is very expensive, but all in all, total cost will not be any more than commercial seat.
Rod