This is actually a tougher call then it looks. Based on talent alone I would have Guillon start with Montana coming in late games to help the pitching staff out plus to play some games against lefties. The problem is, the two of them are going to tire out really fast.
On my SD team the reason why
Morgan Berkman has never made the ML roster is because he gets gassed too easily. Even off the bench I worry he would tire to fast.
I would say start with those two, then when Guillon goes down with an injury, call Beresford up from the minors.