Really all of the above are good focal points. Chin follows shoulder, use high side arm to breath, etc. And as Borate noted, you should be inhaling as high side arm exits the water at hip where rotation completes. The main thing is use a focal to connect the head to body rotation, body begins rotation, head is going with it. Allow the shoulders and high side arm to do the timing, not think about where the head is at in relation to the shoulders/arms.