You have asked a loaded question here and you might want to take a seat along with a big bucket of popcord.
Most efficient - that is subjective though engineer types will tell you otherwise.
IMHO - I like the frog kick for forward movement.
For reverse - I use a reverse frog kick. Essentially this is achieved by pointing your toes down, extending your legs with your feet and ankles together - then bending your knees and sweeping your feet out to the sides. I took a while for me to get this down.
Helicopter turn:
Essentially a frog kick where one foot does a forward modified frog and other does a modified reverse frog. This kick will actually be easier to achieve at first than the reverse frog.
With splits you will likely have some troubles doing the reverse frog. Better to have a full face fin.
Advantages of the frog: If you dive where there is silt - you won't muck up the vis. I use this kick in all environments though. What can I say - it works for me...
The helicopter turns allows you to pivot without using your hands. This is more efficient and if you are taking pictures - it allows you to adjust your view without taking you hand off the camera.
The reverse frog has the same effect as the Helicopter turn in that it allows you complete hands free control. This is really nice if you are doing airshares and are face to face on a long hose, and it works great for photos/ video...
Here are some good videos to help out.
http://www.divetekadventures.com/Images.htm