If a great player is defined by his exploits solely on the field and ignoring the darker side of these great players, then it has to be Diego Maradona for he single handedly inspired his team to 2 successive world cup finals, winning 1 in the process. In Mexico 1986, he scored at least 2 superb individual goals against England and Belgium. Against England, he slalomed pass some 7 or 8 players beginning from his own half. Nobody repeated this feat at the highest level again, and not even Pele could conjour this feat on his own.
If the greatest player also has to be more angellic and less of a devil, then the greatest is Pele. Zidane is a great player and had to face a much more athletic and tactically adept opposition in the present gamen but he has also been sent off a couple of times after venting his frustrations on his markers and tormentors. So had Maradona but I don't recall Pele having to face that ignomity.
Geroge Best? Overrated and overhyped by the British media, much like Gazza and now Shrek.
Other players worthy of mention are Franz Beckenbauer, Johan Cruyff, and Michel Platini. i would say that Romario and Rolando, apart from Zidane, are the present day (and just past) greats also.