Who’s best player on Giants acquired by trade?

This week at The Thirty, in honor of the July 31 non-waiver Trade Deadline, we look at the best player on each current roster to have been acquired via trade. The team didn't draft him, or sign him as a free agent: They simply got him by convincing another team that what they were offering was better than the player being giving up. As you will see, that team was very frequently wrong.