I think this will work out in favor for the White Sox. Contreras should fit in nicely with the Sox because they have many Latino players, plus they have Ozzie Guillen. Contreras should feel comfortable with the team, and he will be out of the Yankees spotlight.
Also, the Sox went after Contreras because they needed a power pitcher, and he adds something that was missing from the team. Contreras has excellent potential, and if the Sox can lock him up, the future is looking good. Over the next years, the Sox will have a solid rotation of Garcia, Buehrle, Garland, Contreras, and Diaz/Schoeneweis.
As for this year, Contreras should do better with the Sox than with the Yankees, and Loaiza will be good out of the pen for the playoffs with his cutter (as a starter, I think he is pretty much figured out).