For a long time, I used 3 fingers (index on LMB, middle on wheel, ring on RMB), especially on Logitech MX500-style mice. However, now I'm experimenting with 2-finger style (index on either LMB or wheel, middle on RMB) to better support the mouse on the right side and see if that helps make me more accurate.
I still have to use 3-finger style on a Razer DeathAdder/Mamba, though. Doesn't feel right with 2-finger style at all, and some people hate it for that. (This is why one friend of mine doesn't use his DeathAdder BE, even though he finds the sensor excellent.)
I'm thinking of getting a Cyborg M.M.O. 7 if the prices drop to reasonable levels, though, and that's yet another very different shape...the only thing that worries me on that mouse is that there's a shift button on the right side that I don't know if I'd prefer to press via ring or pinky finger yet. The only way to know for sure would require hands-on experience...