The busiest domestic/international routes have been revealed by OAG.com based off full-year data from 2017. You can find all the data, including airline and airport punctuality, in the PDF here (published Jan 2018).
I thought it might be quite interesting to have a read through these stats. Might give you some ideas for routes in Infinite Flight! (Apologies for the misaligned screenshots):
Images and Article:
Hope you enjoy! Happy flying as always 😄