As the original poster asked, for next season, I'd go for Bailey. He has a better chance of making the team out of ST than Gallardo, not that I necessarily think he will. IMO, Bailey will get more time in the majors than Gallardo, of course there is still time for this to change.
Long term, I would still go with Bailey. I have 4 pitching prospects ahead of Gallardo: Bailey, Hughes, Garza, and Adam Miller. And then, Gallardo's is right there with Andrew Miller and Mike Pelfrey.