Another thing... the BKK-LAX flight gets in late at night... around 9 or so. This means that you basically have to spend the night (clearing immigration and customs takes time) since won't be able to connect to anything that same night other than the last redeyes to the east coast which won't help.
The times for the UA flights should be a bit better (they get in around early afternoon to most US cities except SEA which is somewhat earlier iirc)