Thats a tough one. Both have good upside. Barry Bonds did say that O Perez was the toughest pitcher that he has faced but Ainsworth pitches for a better team so he should get more wins. Also, I wonder if Perez's arm is a bit tired after pitching so many innnings. It may look like I'm suggesting picking up Ainsworth but you can't discount the fact that a Hall of Fame player, like him or not, said that Perez was the toughest pitcher he faced (don't know if that was ever or last year). Either way thats a huge compliment. Flip a coin or make a trade and free a spot to have them both - who knows? I'm 50/50 on this one.
Swing hard, just in case you hit the ball.