I would say Kobe Bryant. He has a reputation of working hard during the off-season in order to improve his game. i remember one year, he forced himself to make 2000 jump shots every day. In comparison, I remember LeBron this off-season saying he was working on his jumper by taking a couple of hundred shots per day. That fails in comparison to making a couple of thousands. By no means am I knocking Lebron, he's just the only other person I've heard throw out a number on how many shots he practiced (besides Kobe) so I used him as a comparison.
