Both are superstars of different eras. Amitabh Bachchan was the biggest superstar of Bollywood in the era 1973–1992 and Shah Rukh Khan is the biggest superstar of the era 1993–2017. So comparing them on their superstardom and popularity would be wrong as both belong to different time-lines. Hence the only point of comparison between Shah Rukh Khan and Amitabh Bachchan lies in their acting. And in terms of acting, Amitabh Bachchan is better than Shah Rukh Khan, hands down.