The busiest airline routes are short haul routes. In the US that’s Chicago – New York and Los Angeles – San Francisco, though neither of those break into the world’s top 10.
Worldwide the most passengers each year travel between Seoul and Jeju, Tokyo and Fukuoka, and Sydney and Melbourne. By seat capacity Japanese domestic route Sapporo – Tokyo slides into the number two slot.
For long distance routes, based on capacity, these are the 10 biggest routes: