Mitch hit it on the head. Balance and the ability to properly position in the cradle are far more important than exactly where the slings go. If the weight of the boat is sufficient to damage the hull by lifting in slings, i would venture you've got a pretty weak hull, or a Hunter. Just kidding about the Hunter. Before one gets to anal about this, one should consider that the boat is designed to take far greater, and more violent, stresses in a seaway than it will encounter in slings.
In a lifetime of lifting cargo I have never encountered any that reacted well to being improperly slung and then dropped on the dock. Position the slings for balance and ensure they cannot slip. I do not advise "choking" as this will place compression forces upon the deck area. Spreader bars are the appropriate alternative. Your derrick operator will know what they are, and if needed.
“Scientists are people who build the Brooklyn Bridge and then buy it.”
Wm. F. Buckley, Jr.