FOB's on one end, Shuttle T's in 125 grain on the other for me.
As for the penetration issue. Having the shaft diameter be smaller than the ferrule diameter makes for far less shaft drag as the hole made by the broadhead will be bigger than the shaft. Dr. Ashby's extensive research on penetration showed that a broadhead larger than the shaft diameter created 65% of the drag compared to a same-size head and shaft combo.
The physics of a small shaft penetrating better than a larger shaft due to concentration of mass is largely a theoretical discussion; yeah, it makes a difference, but actually seeing it in the field or measuring it is another story.