I ask a variation of this question every year, but it always stimulates good discussion, so we'll go back to that well again.
It is Game Seven of the World Series. You are playing against the New York Yankees in New York. .Your bullpen is burned out from the previous six games, and you really need to get five or six innings from the starter. You can't just pull him at the first sign of trouble, because the bullpen is so worn down that any reliever you put in there has a high risk of being hit hard due to simple exhaustion. Your closer is available, but he's a one-inning guy. You can't pull a stunt and relieve the rookie after one pitch or something tricky like that.
You MUST pick one of the following left-handed pitching prospects to start the game for you.
Robbie Erlin of the San Diego Padres
Danny Hultzen of the Seattle Mariners
James Paxton of the Seattle Mariners
Drew Pomeranz of the Colorado Rockies
Tyler Skaggs of the Arizona Diamondbacks
Alexander Torres of the Tampa Bay Rays
Those are your options. Note that you are not necessarily picking out the best prospect. Rather, who is the guy who has the best chance to give you five or six good innings under these circumstances?