Generally the airports listed first on the featured airports list will be the busiest, so for example:
Hanoi (VVNB), Ho Chi Minh City (VVTS), Can Tho (VVCT), Chu Lai (VVCA), Phu Quoc (VVPQ), Kaohsiung (RCKH), Haikou (ZJHK), Nanning (ZGNN), Yangon (VYYY)
Featured Airline: Vietnam Airlines
Since Hanoi and Ho Chi Minh City are listed first (and are the biggest cities in the list), they will most likely be the busiest.
Route 1: Los Angeles* (KLAX) - San Francisco* (KSFO)
Route 2: San Jose (KSJC) - San Diego (KSAN)
Route 3: Seattle* (KSEA) - Portland (KPDX)
Because these are all famous airports in IF, they will all be busy (but LAX will probably come out top).
Also, how about flying to the less popular airports? I have nothing against you, but it would be terribly redundant if we’re always flying to the same hubs.