I have both A. Harang and M. Bumgarner in my roster and they are playing each against the other this week (@SD) - who would you start out of those two? Heavy punishment for losing pitcher so starting them both is not an option...
I would also go with MadBum, Harang recently came back from the DL, and though he did well against a bad batting team, I don't trust him 100% to keep it up. On the other hand, the Padres usually play well against the Giants and Harang WAS good last time against a bad offensive team, which the Giants are also. Again, I'd still go with Madbum, but those are some things to consider as well.