Zinndl,
To me, the most important thing is being able to put the arrow in the right spot, next would be penetration, and third would be the number of blades. If you are hunting deer, goats, rams, elk, and things of that nature, having hair that won't soak up a lot of blood, two blade heads are fine.
The only other time I prefer a three is on Hogs, Bears, that have a lot of fat that likes to clog the hole, or hair that will act like a sponge. Another factor, I failed to mention, is draw weight. Lighter draw weights are better off using two blade heads for deeper penetration.
Just my observation.