For medium THS, I would suggest you try the POWER STRIKE. From low revs to high rev rate players, and from strokers to crankers, just give this ball a try.
For a long time I was looking for a ball that was similar to the track slash's ball motion - anything that was smooth and continuous. Also, a cover that was easy to adjust. Though the slash had a PowerPlus EX reactive coverstock and can handle more oil than the power strike, it was a great medium THS ball for me. (I'm a stroker with 16.5 mph down lane, less than 300 revrate, low tilt, and medium rotation.)
After 24 games, Power Stirke is very smooth, very continuous, and very controllable. It doesn't jump hard on pulled shots, and comes back when pushed away from the spot. It is also clean up front for a dull'ish looking ball and has a later midlane than the Slash. But, even with the later midlane it is still very smooth when cornering.
Lastly, the thing I like about this ball, is how easy this ball's cover can be adjusted. With the conditions I bowl on and the adjustability of the cover to be tweaked for medium to dry, it'll be all the ball I need for leagues.
Oh yeah......."It hits like a Mack Truck too!! BOOOM!!"