I would vote for ball joint, since i did that very job this weekend. I had to put my ear right on the lower ball joint to be sure where it was coming from and still it was a bit difficult to figure out...
My squeak was prominent 90-95% when turning the wheel left or right and i would get a squeak by pushing down on the bumper. It was so loud people would look at me in the parking lots!
I am now just waiting for delivery of a proper bolt and nut for the pinch clamp to get me back on the road.