I'd rank them in this order:
Oakland has actually done better so far this season than they did last season at this point, and Miguel Tejada and Eric Chavez have not woken up yet, yet they're still winning, once their bats come to life, watch out.
The Phillies offense also hasn't performed anywhere near it's potential yet, yet Millwood has been rolling. He should win 20 for sure this year.
I ranked Prior over Brown, although it's close. Prior will get you more K's is why I would take him first. There is still concerns about Brown's durability, but Prior has also never pitched a full MLB season so it's unknown how he will stand up or if he will wear down in the second half. Dusty Baker has also been doing a notoriously poor job of managing his pitcher's workloads, so that has to be a concern for anyone looking to acquire Wood or Prior.