XL1s sharp or soft shooting?
 

which is better for compositing, in camera setup, full sharpness or minimum?

all the sharpening applied is in-camera modification of the basic image. there's no reason, I can see, to add sharpening in the camera. add it, if you feel you need it, in post.

I've been using the cam with the sharpness fully off/down to get the softer film look but it causes probs in compositing. I thought maybe sharpness or sharper pixels might make it better/easier to composite at the edges. Just a thought.

always sharpness off, edge enhancement can be added later if you want it, it can never be taken away once there as it drastically alters high contrast edges by darkening the one side and lightening the other side to accentuate the contrast edge.