Wait...you mean stirring in extract before you boil, right?
It doesn't matter what you use. You could use a dirty stick that you picked up off the ground. You're going to boil that stuff for an hour and kill anything that could have come off your stirring stick anyway.
For aeration purposes instead of stirring with a potentially bacteria-laden spoon, dump the wort back and forth between your brew pot and your sanitized fermenter. This will aerate the wort and keep it in contact with known sanitized equipment the whole time. In my experience spoons aren't very useful for aeration anyway. I use a silicone whisk for that purpose.