Ive always contended that Vader trains Luke. Sidious actually completes Lukes' training and consequently Luke completes Anakin's just by idealistically accepting death instead of giving into the darkside. It doesnt really matter that his father saved him because really Anakin was saving himself. When seeing it this way it makes it alot easier to delete the darkside/light quagmire you see people running into when arguing what side of the force is stronger and who is the most powerful, or more importantly knowledgeable. How the power and knowledge are used are of course what determine the alignment. Is a point trying to be made by Lucas on learning? It worked, IMHO.