We have used HP, IBM, and a few open-source tools. We switched to Adaptavist as per our organization's requirement.

We use different solutions for different clients. Some clients want to use other solutions, so we use different products simultaneously.

We migrated from Microsoft Test Manager because we wanted to use one tool to manage the development and test product process, as well as to manage our test cases. Jira allows us to have the two together rather than using  two different tools.