The younger guy. Performance when the pitchers were rookies is irrelevant to me. I don't like betting on any 36 or 37 year old pitcher three years from now. Very few pitchers have been worth a darn at age 37, let alone worth $16M. Radke and Santana didn't pitch after age 33. Cliff Lee is 35 and injured. Roy Halladay made it to 35. Roy Oswalt was awesome at 31 and 32 but cooked at 35. Bret Saberhagen pitched 15 innings after the age of 35. CC Sabathia is falling apart at 33. Bartolo Colon struggled from ages 33-36 before somehow coming back at 38. David Cone made it to 36 and he's borderline HoF. There are very few counterexamples and they're nearly all HoF caliber pitchers - Kevin Brown, Tim Hudson, Maddux, Glavine, etc. Mark Buehrle could be another. Do you think 3 years of Shields is worth $25M more to the Twins than 3 years of Ervin Santana? That's all I think you'll get from either pitcher. That's at least 4 WAR over 3 seasons.