Originally Posted by
BadgerBoi
OP didn't limit the question to US airlines. There's a big, wide world out there.
I am the OP. Does Qantas mess with the idea of
lifetime miles any better or more accurately? KLM?
Splitting hairs, United Aircraft and Transportation Corporation looks to have been carrying passengers as early as 1929. Since Delta did not actually carry passengers until late 1929 and "American" didn't go by that name with passengers until 1930, the US crown goes back to United.
I would however make special mention to Aeroflot and China Airlines for surviving inspite of some serious regime shake-ups.