I'd say that these two provided the 20th Century's greatest World Championship matches, given that Alekhine always succeeded in engineering it that he never again played Capablanca after beating him in 1927.
When at his best, Karpov's games wee really magnificent, but it was quite remarkable to see even a great player like him go into "headless chicken mode". In one of the 1986 London games he froze terribly, admittedly in the face of a devilishly difficult position, and lost on time with about 6 moves still to make. I understood that it was the first time he'd lost on time since becoming a professional.
Later, possibly in the Leningrad stage of the same match, all the analysts commenting on the game said Kasparov was dead & buried but he carried out a smash & grab raid in the centre and blew poor Karpov away. I don't think Anatoly was ever the same player again.
It was nice to learn that Karpov, who was always put forward as the Soviet Establishment player, tried to visit Kasparov in jail after Putin banged him up.