The verdict
If you want one place for tasks, docs and hours, and someone will own the setup, pick ClickUp. If you bill by the hour and mainly need to know what the time was spent on, pick Clockify.
They also work together. Project tools hold the tasks and Clockify holds the hours, and it connects to accounting tools. I ran ClickUp at my own agency for about a year. The visibility was a real gain, but some colleagues found it too much. For a small service business that bills time, I would start with Clockify on the free plan, and add a task tool only when coordination becomes the bigger pain.