Yankees- Bobby Abreu- Abreu started off the year very very slowly. He hit only about .260 in the first half and was earning a lot of criticism for his fear of the walls on defense. Not coincedentally, when Abreu started hitting the Yankees started hitting. This slow start was widely attributed to him being out of shape in the Spring Training. Also, if you remember he had an injury in Spring Training last year. All in all, by the end of the year he ended up with a respectable line of .283/.369/.445. Good enough for him to get his one year option picked up by the Yankees. His defense is starting to become a flaw as well. Abreu is supposedly in great shape this year and A-Rod predicted a big year from him. I`m a little skeptical but you never know. He`s a solid stop-gap until Jackson or Tabata are ready but he`s likely to be gone after this year.
Red Sox- J.D. Drew- Drew was another one of the big signings last year by Theo Epstein. I didn't like it (well, as a Yankees fan I liked it a lot ;)) at the time because of his injury history. However, Drew has a ton of potential, when he is healthy he is a good player. Last year he was healthy but was still a dissapointment. His defense seemed to take a dip (though this may be a fluke). His power also fell. He had a big role in the playoffs though and still has time to make this deal worthwhile.
Conclusion- Yankees- Strangely enough, I give Abreu the advantage mostly based on his power advantage. Drew has a very slight advantage in OBP but Abreu actually has more power. They are identical for their careers but Abreu was much better in 2007 and slightly better in 2006. Abreu has also been doing this for a long career of consistency. Drew is still an injury risk.