I love the public library. I get to go in and grab any book they have and read it for free(I pretend my taxes don't count)! Wow. That's amazing. But that's assuming someone hasn't checked out the book i want. Sometimes i have to wait for a book and sometimes I am too impatient and i just buy it from the Bookstore.
See the Bookstore has tons of books, not as large of a variety, but usually they have what i want. Often if I want a book they don't have, I can ask for it and they work hard to get it for me asap. Plus, i don't get some crappy fees if I'm late returning the book, because its mine.
I feel like the same thing is true of JIRA to Bugzilla. They are both great bug trackers, but their nature is totally different. You pay for JIRA (unless you're an open source tool) and no one (not even Mozilla) pays to support the development of Bugzilla. Lots of organizations and individuals donate time when they can, but there isn't any money being exchanged from a "bugzilla org" to other folks.
I feel like this by itself makes the comparison not exactly fair. Now if that philosophy isn't an issue and neither is money.
JIRA's UI is cleaner/nicer but not as geared around power users in many people's opinion, but it doesn't support the patch review process as nicely.
To be clear i've used both systems. There are PLENTY of super annoying little things (which maybe jira fixed in this next release). But as someone who has now come to understand JIRA really well and its limitations and understanding bugzilla and its limitations, I'd pick Bugzilla, but most people I work with, prefer JIRA every time.
Maybe JQL will fix the biggest JIRA issue, advanced search, but in the end, I like bugzilla because although admin UI for bugzilla is weird, I honestly find it easier to use (once I understand the mental model) than JIRAs. Oh... also, JIRA's email system makes me want to shoot somone, can't add other people to cc lists, and I couldn't for the life of me figure out how to turn off emails for specific bugs, it seems like some crazy all the things in a project or none... but that's again a personal issue.
But I'll continue to use JIRA at work, and figure out how to make work-arounds for "adding others to the cc-list" and other issues. But if you're reading this post as a way to find the answer to this question. Ask yourself this: is money not an issue? Do I have lots of novices using this tool? If the answer is yes to both of those, JIRA might be the way to go.
If you've got experts who will live with this tool every day, would prefer emacs, the command line and grep to Office, and want to be able to hack and slash their way to happiness... Bugzilla is probably your solution.
... Search is still horrible! doing a search for a bug with a specific owner between 2 relative dates results in "error" with no error message. OMG i miss Bugzilla. Plus quicksearch in bugzilla is GREAT @username gets me all their open bugs done... jira not so much. :(
my 2 cents