It seems that a few people responding here fail to understand that this is a popularity contest based on member’s input. There are no shortage of great drivers in the history of motorsports. Just because a driver wasn’t included in the list of 6 does not make them any less successful of a racer.
While I would not expect him to show up on a short list of all time favorites, the figure in the work of racing that I really admire is John Surtees. He won four Grand Prix (motorcycle racing) World Championships and later went on to win another World Championship in Formula 1 racing. Winning championships at the highest level of both motorcycle and automotive road racing is an accomplishment that likely won’t be repeated any time soon if at all.