My own personal greatest will always be Gilles Villeneuve, the fastest and most naturally talented driver ever to sit in a car imo, but the greatest F1 driver in terms of the perfect balance of all the attributes required (of which natural talent is only one) it has to be Senna, I dont really see how anyone could think otherwise tbh.
What people often overlook is the fact that in the period that he was winning his championships/poles/races, he was competing against the likes of Prost, Mansell and Piquet.They already had a load of world championships and god knows how many grand prix wins between them when Senna arrived in F1 as a rookie. He didnt have it relatively easy like Scummy did.
When Senna moved to the F1 big time by joining mclaren as Prosts team mate, Prost was already the most succesful driver in the history of the sport - then Senna destroyed him, he was simply on a totally different level to Prost and everyone else really.
The only one who really gave him any serious trouble was Mansell, because he was so brave and gutsy he never backed down from anything or anyone.