Originally Posted by
seawolf
The passport information you enter can be changed when you check-in during subsequent flights at the check-in counters.
I think your first flight out of the US should be the US passport (assuming visa free entry at destination). There's a thread on the US State website stating that dual nationals must depart/enter US on their US passports.
Is the OP a US dual-citizen?
It is indeed best to exit the country using the passport which was used to enter the country. Just as it is best to enter the country using the passport which will be used to exit the country. While some circumstances may change the ability or desirability of doing that stated earlier in this paragraph or elsewhere in this thread, alternatives may also work lawfully under a variety of circumstances.
Don't necessarily take everything on a government website or presented as a stand-alone legal reference in statute or CFR as generally representative of the entire body law applicable to entry or exit. A lot of things presented by or on behalf of government are oversimplifications presented so as to make life easier for one or more involved parties rather than a presentation of what all is lawfully allowed .... without court-sentenced punishment. Government websites are often dumbed down to make oversimplified representations, and this is an area where that is the case too.