Depending on your exact definition of medium oil, the XXX Factor should handle more oil, and probably hook more. It is designed for medium to med/heavy oil, medium rg (2.52) and pretty high diff (0.055). The Thing Returns is made for med/light to medium oil, a little higher rg (2.56) and less diff (0.045).
A profile would help a lot - rev rate, ball speed, PAP, tilt, type of lanes, amount and oil pattern... A cranker would want a TR for medium oil. A low level tweener like myself would lean towards the XXX.
I don't have a TR, but I have the Thing. Great ball.
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Ron Clifton's Bowling Tip Archive