First, make sure that you have done a HUET course, so you have a chance of escaping when it goes belly up (not a question of IF but WHEN). Even with floats, they will buy you time at best.
Then it depends on sea state, wind, type of helo and its CoG. I have been taught that if you anticipate a rough landing it's best to stick the tail in to absorb most of the impact forces.
What it does to the main rotor and wheter they will come crashing throug the cockpit, I don't know. But to nose is is certain disaster.
Furthermore, If you're machine has hydraulic controls, make sure you don't position the controls in such a way that your left leg gets physically trapped. To survive you need to be able to exit the aircraft..so think also about wearing a helmet.
And finally, you need a bit of luck. And survival kit to keep you alive outside of the aircraft in a hostile environment like the sea.