There seems to be some doubt as to whether Marshall can stay healthy for a full season. I think his upside is a #4 starter, because although he has great control, he doesn't have the stuff to be more than slightly above average for a full season. Gallagher, on the other hand, has a plus curve and a pretty good fastball. He is definitely the less-proven of the two, but with a considerably higher upside. Marshall's value is as a spot starter/long relief guy IMO so it depends on what the GM in question is really looking for.