Fischer has to be considered the greatest. His run through chess was fairy tale in its rise. Kasparov's dominance was longer I guess, but if Fischer kept playing he would of ran through Karpov for another some odd years. I don't know much about all the seconds that helped Kasparov, but Fischer did it on his own more than any other player. I refuse to give too much credit to "team Kasparov" however. Surely he was great outside of the books, his sacrifices are part of what make his games so appealing.
This is not about playing the "What if?" game. This about who is actually better based on what actually happened.

Fischer has to be considered the greatest. His run through chess was fairy tale in its rise. Kasparov's dominance was longer I guess, but if Fischer kept playing he would of ran through Karpov for another some odd years. I don't know much about all the seconds that helped Kasparov, but Fischer did it on his own more than any other player. I refuse to give too much credit to "team Kasparov" however. Surely he was great outside of the books, his sacrifices are part of what make his games so appealing.