This is probably going to be wildly unpopular, but if you take all factors into account (quality of competition, development of new pitches, integration of the majors, the influx of the bext players from around the world, professionalization of sports, improvments in modern medicine and training, etc) the best hitter of all time is probably Barry Bonds. Enjoy him while you can, so you can tell your kids and grandkids that you got to see the best hitter of all time.
Scot.