I'm currently working on a remodel and going to insulate the floor with R19 per Title 24 out here in California. Planning to later install 3/4" oak throughout the house. When selecting the insulation, should I use faced (w/ vapor barrier) insulation or un-faced? I will definitely put a vapor on the subfloor before laying the hardwood, but am unsure about the vapor barrier for the under floor insulation. My concern is that if I use two vapor barriers, I could trap moisture in the subfloor. Should I simply use, un-faced insulation under the floor to allow the subfloor to breath?

Nothing other than 15# felt paper (or that new fangled breathable plastic made to replace it) under the wood. That means you can use any sort of insulation you want.