LIke comparing any stars/ athletes from different eras, this is a bit of a subjective exercise... but generates a fun conversation, nonetheless.
My first thought is that a good case can be made for Kasparov. Not only was he champion for a very long time, but by his involvement in public affairs, his writing (beyond chess, as well), and his general outgoing demeanor - I think he would probably get my first "vote".
Fun topic; thanks for starting it.
I would say Bobby Fischer because everybody's heard of him. Interesting topic.
Mikhail Tal is not one of the greatest. But he is contender for the most popular WCC. His magical chess plays beat Botvinik, Smyslov, Spassky, Fischer and Karpov. Tal is the Houdini of WCC.
Had to pick one, I'ld say Carlsen.
He has that Matt Damon/Justin Bieber thing going. So the girls like him.
I would say Garry Kasparov. But he was so political he alienated many.
I think that Tal is the most popular among chess players, because he created the biggest number of tactical masterpieces with sacrifices. But Fischer is definitely the most popular among people who do not play chess. The reason is politics. He was the only representative of the west who was stronger than soviet players. High level of chess was one of symbols of political power in the Soviet Union.
Who do you think is the most popular world chess champion? Explain your choice.