I like Trac better. It has a more intuitive interface, and with the various plugins you can argue it does way more.
So why did you switch to FogBugz?
If I had to guess I would assume that a manager/rest of team set the bug tracking software system prior to his arrival.
If Trac has a mass-add option like Fogbugz does, it sure wasn't obvious. Entering 50+ bug reports with Trac, like most other bug tracking software, is a pain.