This is an interesting read:
Ditching Myths
Myth 5: In A Retractable, It's Better to Ditch With the Gear Up Than the Gear Down
This one has sparked more hangar arguments than debating over pitch and power. Here's our view: It probably doesn't make much measurable difference. Or, put another way, if you think it does, show us some data.
Unfortunately, the accident records shed no useful light on this controversy. Pilots often don't remember whether they extended gear and/or flaps; they don't recall if they landed with the swells or upwind or crosswind. Even if they do remember, this detail often doesn't make it into the accident summary.
We think the best you can do is to examine the big picture: Irrespective of aircraft configuration, do the pilots and crew get out of the airplane after impact? Yes, overwhelmingly. How often does the airplane flip over because the gear caught in the water? We don't really know. But even if all the airplanes flipped--highly unlikely--the occupants still manage to egress safely. Conclusion: It may not matter much.
From films of live ditchings and interviews with survivors, our impression is that most airplanes don't flip, but dig in one wing, turn and settle upright or settle straight ahead with a bit of nose under moment. But, we simply don't have enough reliable information to make a definitive judgement on this. Our best advice is make your own assessment and configure the airplane accordingly.
More critical than configuration, in our view, is touching down parallel to the swells, or if that isn't an issue in calmer water, landing into the wind or with the river's current to yield the lowest possible touchdown speed.
Worth noting is that 9 of the 22 fatal ditchings involved retractables. As with the high wing versus low wing controversy, these numbers are too small to draw any meaningful conclusions.