This is a question that divides bowhunters. While largely a matter of personal preference, there are some physical considerations. If all other things are equal (weight, sharpness, aerodynamics), a two-blade mechanical broadhead will penetrate more easily than a three- or four-blade model. If you have a comparatively low draw weight bow, a two-blade head is more lethal.However, modern compound bows are capable of producing tremendous power – driving any head with more than enough force to be effective. In that case, three- and four-blade heads (the latter are usually fixed or hybrids) will maximize penetration, tissue damage, and blood loss, so you're more likely to deliver a kill shot.