The general consensus is that lens-based IS is better. The reason for this is that each focal length of lens requires a different amount of stabilization. Longer focal lengths require a much greater amount of prism movement to stabilize the image than shorter focal lengths do. By building IS into the lens the IS can be specifically engineered to be optimal for that lens' focal lengths.
One of the supposed "pros" of in-camera IS is that lenses are cheaper because they don't need to have IS. In my experience this isn't true. For some reason, Sony's lenses cost the same as equivalent Canon or Nikon lenses.
