I would think the best grip will be the one that works best for you. There, that help?

Seriously though, for me, I use all three that you mention plus others depending on what I am trying to do with my playing. I'm sure other people here will have more detailed information on the benefits and drawbacks of each grip but you may want to just pick one and go with it until you get comfortable with it. If you find you can't play what you want, try a different grip. I would think being able to use different grips in different situations would be beneficial.
I personally have evolved to use the first joint of the index finger as my fulcrum. If I can describe it in more detail...
Palms down, but not flat. My hands are at about a 45 degree angle (if you laid a ruler across my knuckles, the outside edge of my hands would be down close to 45 degrees).
I point my index fingers out almost totally straight, then bend at the first knuckle to wrap around the stick. My thumb is to the side of the stick (sometimes moves closer to being on top) to loosely hold the stick in place. Takes a lot of practice to build up the thumb/hand muscles to have a firm but loose grip I found.
At times, my finger/thumb grip can be defined as my thumb actually touching the tip of my index finger (very loose fulcrum).
Hope that helps
