Unless you are flying to Korea as your final destination, I would check to see what your layover in Seoul will be on your return. In my trips to BKK over the years, I have always avoided both Asiana and Korean airlines because of the looooooooooooooooong layover on the returns at the old Kimpo airport. Even though they provide a room for you to rest, the last thing I want on my return flight is a 8+ hour layover.

CS