As a Calgarian who has lived in Thailand for a while, and now Singapore, I have flown many airlines between Thailand and N. America. Not sure if you have bought your ticket yet, but here are my tips.
Cathay Pacific is quite good, I don't really care for the capsule style seats, but the food and service really makes up for it, and if I had to choose them or an American carrier, it would be Cathay Pacific for sure!
Thai Air is also worth paying a bit more as well, especially if you can get a deal on there Premium Economy seats, which are fantastic, and often not that expensive!
You also may want to look at prices into Phuket (HKT) as well.
Korean Air flys there from ICN, and I quite enjoy there service as well. And Phuket is a nice place to start Thailand from, you can relax on a beach first instead of the hustle and bustle of Bangkok.
Enjoy your trip!