.....and to be honest it depends on your reason for ditching.
The best chance of survival is to make as controlled an impact into the water as possible and let the auto inflate decide when to deploy the floats.
Many years ago a ch46 driver on an unplanned rapid decent deployed the floats before hitting and tore the aircraft in half along the centre like it had a zipper. it makes exit very rapid but through the door is better than through the floor.