Between the two, I'd rather hold on to Swisher. Despite a lower batting average, he has a signicantly better on-base percentage, is younger, a switch-hitter, and plays 1b (unlike Nady).
UPDATE Jan. 9, 1:13 pm:
Brian Cashman has received more offers for Swisher, but is more amenable to trading Nady.
- The Red Sox signed John Smoltz and Rocco Baldelli. Along with Brad Penny, they're taking chances that they rebound from injuries and/or poor years.
(h/t to MLBTR)