I'm interested in evaluating bug trackers, but I wanted to back up and figure out what sorts of criteria were most important in bug software. So far things I've thought of include:
stability
cost
Any ideas?
Ease of use
This should, in my opinion, be on the top of your list of features to evaluate against. You want inhouse developers and testers to take any and all things they notice in the software and plug it into the tool, even if they're currently working on something else. For this to happen, the tool must be so easy to use that it stays out of the way and just takes your data. The worst bugs are those you don't know about.
A tool that has 15+ fields on the screen, where 10+ are required in order to just be able to submit the issue, is not such a system. With such a system, you'll get postit notes from testers to developers about the little things.