Ask HN: What issue tracker do you use?

This comes up periodically, but it's usually centered around a review of a new tool, or a particular tool.

I have to admit to being a jira lover inspired by http://news.ycombinator.com/item?id=3000200. With so many people posting polar opposite experiences, I wonder:

What issue tracker(s) are you using?

For what sort(s) of projects?

How default/custom is your installation?

How many other issue trackers did you try, if any?

As always, the "and why" information is nice, too.