I can't answer "best" - that's subjective and depends entirely on what you need from your reporting.
For an opinion, I'd say Tempo is a very popular, powerful and friendly timesheet system for JIRA, but I'm quite fond of Andriy's Timesheet reports if your focus is just on reporting.
Have a read through the results from https://marketplace.atlassian.com/search?query=timesheet
I’m a designer on the Jira team. For a long time, I’ve fielded questions from other designers about how they should be using Jira Software with their design team. I’ve also heard feedback from other ...
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