... what your favorite medium bore is and why.
For arguments sake lets say between .32 cal and .40 cal is medium bore ...
My favorite rifle/cartridge is my .300 Weatherby. I would not hesitate to hunt any North American animal with it. I never considered the .300 Weatherby as a small bore cartridge but with the parameters of this thread, I guess it is.
So within these parameters, my favorite medium bore rifle/cartridge is my .375 Ultra mag. This cartridge has the trajectory of a .30-06 and the energy of a .416 Remington.
I've taken my .375 RUM on two African hunts, and used it to make one shot kills on a variety of animals from 25 lb Steenboks to 1500+ lb Buffalo and Eland, at ranges from 30 to 350 yards.