I've been a bugzilla user for several years since that what my Dev. manager decided was best but a lot of new projects use Trac, and it definitely seems a lot better. Trac's bug tracking features might not be as sophisticated as as Bugzilla, but Trac does more that bug tracking. Trac has an integrated Subversion browser and wiki, so it provides a complete platform for collaboration between developers and users. Newer versions of Trac will support other revision control systems through plugins.

Trac has a much better user interface. Trac is better looking and friendlier than bugzilla, the freindliness might come and the expense of advanced features found in Bugzilla, but it shouldn't be a problem for most projects.

Bugzilla is a mature product used by giant projects with tens of thousands. I doubt any Trac projects will ever get that big, it would take a long time and I doubt a project that size would want and integrated wiki.