A guy in Africa has been doing research into lethality in big game with almost every broadhead ever invented. His name is Dr. Ed Ashby. Do a quick look online and you will probably find more data on the subject than you can comfortably wrap your head around.
On the one side of the spectrum you have mechanical broadheads with a painfully pathetic showing. Specifically, the Rage broadheads suffered a 100% mechanical failure! Stay away from mechanical broadheads. In fact, give up hunting completely rather than use mechanicals.
The other side of the spectrum is the rigid, fixed two blade broadheads. The best of these would be the ones that cut on contact and are sharpened on one side only on each of the blades. The blades should be hard enough steel that the point does not bend or deflect. Hard steel is hard to sharpen, but maintains cutting edge better than softer steels.
Whatever you chose, learn to sharpen these blades with a water stone or oil stone. Get them sharp enough to slice cleanly thru cigarette paper and you will have a deadly arrow.
