Do you know where you are headed in Thailand? If you can only fly AA then HKG would be your best option with ICN coming in 2nd.These two airports would have the lower costs airlines to get into/out of Thailand.Example is I paid around $120 for one way BKK to ICN last year on Eastar Jet.
Anyways, if going to the Bangkok area remember DMK, normally has cheaper flights.
If going to the beaches around Phuket then HKG is probably best option. Just know what airlines you can fly out of ICN/HKG and prices and keep an eye on AA flights to/from each place.You might have to fly into HKG but out of ICN or vice versa.
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