You do not have to avoid it unless you are over 3 months at an immigration unit where they specifically check. I have trippel citizenship- no problems. Only thing is if you enter with one and leave with the other at a place where you need an exit stamp it can be tricky coming back. Or if they wonder how you came in if you are using a different passport for exiting than entering (not usually but may occur in places like Vietnam).

According to US law US citizens holding US passports must enter the USA with their US passport. In practice though it doesn't matter. Be happy you are lucky even better is if you change your name in one of them- that way if you ever get into trouble it is easy to escape.