I like using the NAP Gobbler Getter broadheads. They are mechanical and have more of a rounded bullet point for bone-crushing instead of a sharp point for the cutting. Cutting diameter is 1 1/2" with 3 blades.

Try for your shot mid-way thru the wing section for broadside shots(some people recommend just a little low and back to try and clip one or both of the legs) and dead center of the body/back if the turkey is walking away from you.