So many good champions... Clark, Senna, Prost, Fangio, Stewart, Lauda. If you go by ratio then Clark and Fangio have the best records I believe. However Stewart was brilliant on and off track when he did a lot to improve safety for the benefit of the whole sport. Then you have Senna and Prost who really shone in an era that was full of fantastic drivers but had questionable ethics. There's also the point that unlike the 21st centuary poll this poll spans 50 years of Formula 1 when the technology has changed drastically in each decade, this makes any comparison of the drivers really difficult to make because different generations have different chances and opportunities that previous generations simply didn't have.
For that reason I can't really vote, what is interesting to note from my selection of drivers is that each decade is covered by a driver... except the 90s. Each of these were brillirant for their own different reasons Fangio drove the big, heavy but powerful cars of the 1950s and put his life on the line each time he got in the car (as all of these drivers did (it was in the 90s in which safety has almost ruled out death). Clark could race the wheels off anything and I have no doubt that he would have won more than 2 titles. Stewart was a great champion, fanatastic both on and off the track. I also rate Lauda highly, not just for winning 3 titles but because he retired came back a few years later and beat a top notch (Alain Prost) team-mate to the title in 1984 by half a point. Then there's Senna and Prost, both were rated highly for different reasons. Senna for his undoubted speed (1.5s faster than Prost at Monaco '88) and talent in the wet, whereas Prost was renowned for his consistency and ability to look after the car.
One thing I dislike about these comparisons is the 'death' factor, I often find people rate the drivers who died racing higher than they would if they hadn't died behind the wheel. Anyway I won't be voting because a comparison of half a century of racing is impossible for me, but in each individual 'era' of racing these are the drivers I consider the best.