Although my wife has bowled on leagues, she does it mainly just for fun. She recently entered and won a drawing for a $300 gift card good at the local pro shops, so she decided to get a new ball. She throws straight, fairly hard and with a conventional grip. So we talked to the pro shop operater and the first ball he recommended was the Cyclone. His reasoning was that even though she throws straight, a reactive resin ball is just better than the plastic balls. Better reaction, better pin action, etc.... And in the event that she starts bowling more seriously, it's a ball she can "grow into". Made sense to me. So we went to a big clearance sale the pro shops were having this past weekend and she left with a Stike King.
So while I'm not as experienced a bowler as most here, FWIW, I'd say go with an entry level reactive resin ball.
Good luck!!
Failed to mention that my wife currently throws an old Columbia Galaxy.