Who was better, Fischer or Kasparov?

Who was better, Fischer or Kasparov? –@StockSage1

At his peak, Fischer was better relative to his competitors than Kasparov ever was. However, if you paired them at their respective peaks (using a time machine: then Kasparov was better). Why?

A)    Training techniques improved

B)    Computers enabled Kasparov to do quicker and more extensive research on any position

C)    Kasparov was never mentally ill so he was able to pursue studies and play in tournaments for 25 straight years. Fischer maybe had 10 years of study.

D)    Kasparov was already recognized as a young talent at the age of 9. Fischer had to work harder to get his  talent out. Kasparov also had better trainers at a young age. Fischer had none.