For most UK pilots I guess that the most likely bit of wet stuff we are likely to ditch in is the English Channel. From too many hours spent trying not be seasick sailing across said channel I would make the following observations:
1. The Engish Channel is rarely calm enough to allow any kind of precision fly in.
2. Due to tidal effects, there is rarely any really regular wave pattern although it should normally be possible to land roughly across the waves. This will depend on the relative directions of wind and tide.
3. I seem to remember being told to try to land, across the waves, aiming for the back of the wave. With the irregular chop you tend to get in the channel I think that is going to be a matter of luck.
4. Those of us who do fly across water should know before hand what is the best way. It's a bit late to change your mind when you get close to the water.
I do hope that this thread attracts some informed opinion. I guess that, at the moment I would land crosswind, across the waves. At least the drift would be in the direction of the waves and might reduce the impact force.