Most I can help you is I have a Gravity Shift, and my wife has a Kinetic Energy.  From what I see the Kinetic Energy is a bit earlier and smoother.  The Gravity Shift is all about backend.  Both would be great on a THS.  The Kinetic Energy may be a slightly better ball just because it's a bit more versatile, but if you have friction to the outside, and good backends, you may not miss the pocket all day with the Gravity unless you get a little slow with your speed.  My pick.....the Kinetic Energy, only because it may keep you out of trouble a bit more, and can be used on a little wider variety of lanes.