Fiberglass is generally glued while aluminum is riveted. Fiberglass can delaminate or bubble if the construction was faulty, while you won't have that problem with aluminum. As for cleaning, we have aluminum and it's easy to clean, but I don't think it's any easier than FG. Aluminum is generally painted too while FG has the base color built in.
Generally a toss up as to which is better. However there was one coach manufacturer that had Aluminum sides and steel cage and used steel rivits causing corrosion around the rivits do to dis-similar metals in this case it was a bad deal.