Zephty offers a Jira plugin that does test case management (note, in the past, I have done some work for Zephyr. But I have worked for a lot of test companies). If you are managing testing through test cases (formalized documents that track specific steps to risks based on requirements) and using JIRA for requirements, it allows you to keep all that information in JIRA. If your work is more exploratory, charter or emergent-risk based, I'm not sure how much it will help. I believe it has a free version for up to 5 users; give it a try!
When using JIRA make sure you are careful to set up the different sub task and attributes. JIRA can be used for defect tracking but make sure you have the appropriate are set up at the beginning. Also have the team to use the different priority levels when creating defects as well. This will allow you all to track the defects back to a root cause and can be helpful to the Development and QA management team.
In my experience Zephyr for Jira is meant for small teams, it does not scale well and in bigger QA teams / organisations reporting is critical that is a big weakness with Zephyr for JIRA.
Another major area of concern is maintenance of test cases in Zephyr, it takes more time and effort. In case your product is stable then this a good tool but if there are more features implemented in short build cycles you will find Zephyr cumbersome to use.
