I maybe grab Wandy as he tends to have great second halves and could pay off down the road. If you are more interested in short term help, I think Myers is rolling along pretty nicely.
I was leaning towards Wandy, because high strike out pitchers have huge value in our league based on the scoring details, however I'm not too familiar with Brett Myers. Of course I know who he is, but I don't watch many Astros games. Is he a legit ace? I am concerned by the amount of home runs he gives up and his lack of high strike out potential. Seems to me that while he is the ace, Wandy is the better pitcher. Am I wrong? Also, has anyone watched any of Volquez's games this season? Has he shown any sparks of his past success at all? I really like his potential to put up big strike out numbers.