According to my old aeronautics professor, 2-blade turbines are the most efficient when pointed directly into the wind. They've tested 3-blade, 5-blade, and vertical turbines and couldn't get the same amount of output. These experimental turbines look great on paper but rarely scale up.

The reason why 3-blade is the most common design is 2-blade turbines induce a lot of harmonics at high speed. 3-blade cancels it out but are slightly noisier from the blades slicing through the spoiled air.