I'm using https://www.temponia.com/. Very simple, not that expensive, excellent support and — and this is the reason why I picked it — Xero integration. It doesn't look as nice as the competition, but a lot more flexible and helpful than the competition nonetheless.
We're not asked to track time, but I started using https://wakatime.com personally at home and it has been awesome to see how many hours I've put in over a weekend or whatever. It integrates really nicely with VS Code too - after setting it up the first time I don't even notice it running.
I hardly ever (maybe never) bill per hour/day so I have no need for time tracking from a client perspective. I however track my time for two reasons. First, I am able to work out what my hourly rate actually is, but this is for my internal usage. Second, always valuable to go through the process on a project and understand what worked and what did not. Excellent way to turn your learning about a project into processes. In terms of software, I have successfully used Toggl, and currently testing a more automated way to track with Painless Time Tracker https://painlesstracker.com/