Only one ball plus a spare shooter?
Two words: BLUE HAMMER. Unfortunately, they're not made anymore. The next best made right now would be one of my favorite balls that I own, the Black Messenger. Two piece urethane, it comes sanded about 800 grit. Columbia touts it as a dry-lane ball (as all companies tout their urethanes, in my opinion the only reason is because it sells resin balls because "urethane balls don't hook"--yeah right), but I've used it in fresh oil and it DOES do a good job. There are also 3-piece variations on the same theme: Black Scout, Groove, Purple Claw if they still make it. Some of the three piece dull resins will act like soft urethane also. I had a Green Claw sanded that I could've sworn was a green Burgundy Hammer.
Again, and I stress that IF it will ONLY be this ball and a spare ball, I'd go with urethane. If you must go with resin, get a milder one.