The verdict
If you have to choose one, I'd start with Google Calendar when you are on Google Workspace, because every team needs a shared place to book meetings. I'd choose Toggl first when time is your product, for example in an agency or consultancy that bills by the hour or quotes from past projects. A calendar will not tell you why a project overran, and a timer will not stop two people booking the same slot. Most service teams end up with both. The calendar shows what was planned, and Toggl shows what happened.