Somehow the only good things I heared about them came from people who made their money by building stuff they wanted to sell on the Atlassian platform. People less biased always choose alternatives.
I can't say much about them myself. I only used Bitbucket, because of the free private repos. Their UIs are pretty mediocre, but I use it via Git cli, so it doesn't matter much for me.
After Atlassian bought them:
* The service I paid £5 a month for became free
* The stability issues started to improve in a dramatic fashion
Today Stash is a great product (IMO), and BitBucket has really improved from having great Jira integration.
I was actually sad because I couldn't justify paying for the premium features (multi-person private repos) in the same way, because it was nothing I needed. It was the best £5 subscription I ever had :)
JIRA has its quirks but it's very flexible and customisable. Its UX is also quite ok for such a complex piece of software. Keep in mind they're competing with stuff like SharePoint and downright UX atrocities such as HP ALM.
Confluence is among the best enterprise wikis targeting end users (i.e. users not familiar with Markdown), too.
We use Jira since the early days, and are quite pleased with them.
So far, all the other systems I have used were all worse than Jira.
