I sell the resin and gel coat to the boat builders and I have a huge % of the market, almost every builder in the area uses my products, although I must say over the last few years the number of customers has dropped off dramatically, not many survived the down turn. Aluminum boats builders seemed to have survived the market conditions much better.
I have both aluminum and glass boats, and boats made from each material can be made to perform fairly well, but glass has the edge in ride and performance. This is because a glass hull can be built to the exact shape the engineer/designer had in mind much easier than aluminum, not that aluminum hasn't made some good strides in recent years.
Glass not only has the possibility of the deeper V, or whatever convoluted shape the builder wanted, but it also flexes slightly, which absorbs and dampens the impact better.
Some glass boats have no wood in them and most that still do use treated wood with a 25+ (some lifetime) warranty against rot. So a well built glass hull should last a very long time with few issues related to salt or fresh water. Aluminum should last a long to time too, but crevice corrosion can be an issue and a simple fresh water rinse can help, but doesn't totally eliminate the problem. Fatigue can be an issue with aluminum too, depending on the design, grade of aluminum, skill of the welder and how the boat is used it can develop cracks, and welding the cracks may only be a temporary fix.
My customers make many of the charter boats used in Alaska, these guys pound out to the fishing grounds every day and the opinion on which material to use depends on who you ask, the skippers, or the charter business owners. The skippers like the glass hulls better because the ride can be much better, the owners like aluminum because the up front cost can be less, plus being lighter they may get better mileage.
Like Nelly said, there were glass boats built to a price point, and that price point didn’t necessarily include quality of construction. The purpose built glass fishing boats tend to hold up very well.
My jet boat is aluminum, my drift boat and bay boat are glass, I would have no problem owning an aluminum boat for the salt though.