Personally torn between quite a few drivers. In the end voted for Surtees, only because at the time of voting he had a bit fewer votes than some others.
Hard to choose between Surtees and Rindt. I think they were team-mates in Cooper and Surtees had a bit of an edge then? But obviously Rindt hadn't reached his prime yet. Which arrived a couple of seasons later, though obviously that didn't last long.
People's careers were different then and obviously with someone like Andretti you wonder, how much more he could have achieved with more full-time F1 commitment. But he did well with the time he had in the sport.
Obviously as mentioned by others, comparing eras is very difficult. Because fast forward Mansell is from a different era to these guys. And then further forward Raikkonen, Button and N.Rosberg are again from a different era. What these guys have in common is that they were all very good drivers in their own right, but a few drivers go into the history as greater than them from their respective eras. But if you like, you could give a point for Mansell in terms of longevity.
I think Keke Rosberg was actually very impressive from 1982 to 1985, but his reputation has suffered from a poor 1986.
Interesting point. Looking at individual title-campaign seasons of these drivers, Keke's may well have been among the most impressive ones on the list.
Also wonder if drivers like Jones and Scheckter go a bit under the radar on the poll. Maybe not as spectacular as some others, but they still put in very good seasons on their heyday.