WhichWay2Go
Registered Users (C)
it is ok to use country X's passport to enter country X and use US passport to return to USA.
That's the whole point of dual Citizenship. You use the US one to leave here and the other Passport to enter your birth country and there are no Visa or length of stay restrictions. If you used the US Passport to enter your birth country, you would be restricted to a visitors Visa.