If you can find out what this film is called and find it with some subtitles you can read too, i highly recommend watching it:
http://www.youtube.com/watch?v=udF8q9kzJ4o
Documenting Zizou's last game for Real a few months before the final. Real intimate look in at his personality, life and family. Terriffic stuff, and in fact really wins me over in regards to "the best footballer" thing.
One can always discuss greatness at varying conditions: did he score more or win more trophies or whatever, but for me it's all about the culture and aesthetics of it - after all, football is culture as much worthy of a museum as a found-art-pisspot. And in terms of creating history, beauty in football and of course drama, Zidane gets that nod in front of most other 21st century footballers.