I have had 2 tractors with a hook mounted in the center of the bucket. I think this is the best place for balanced lifting. If you put the hooks on the sides you are not going to be as stable as you lift your load higher. Also a hook in the middle makes moving 3ph implements with the fel easy, just attach a chain to the hook and to the pin where you would normally hook the top link, position the cutting edge against the frame and curl the bucket.
On both buckets I have used one of the heavy duty hooks normally seen on full size backhoes. They have both a slot to lock the chain in and a loop for tie straps, etc.
JT