Feliz has the better glove and arm, but DeRosa can play more positions. Feliz hits for better power, but DeRosa hits for much higher average. Both are about the same age.
Overall, I'd have to give the edge to DeRosa because of his hard-nosed style of play. If I had a very good offense, however, and just needed a solid glove to anchor my infield, I'd go with Feliz. DeRosa is a good guy to back up at third, but his glove will cost you some runs if he's out there for 150+ games.