Clockify

This solution is great, easy to use, have great functions to export reports to excel to perform analysis, nice and powerful dashboards, and almost no training needed for the users.

Really we can´t find Cons for this app, the only issue is that the timesheet feature is not shown by default, but you can simply make it appear with a little of research.

The interface is nice, the reports get me what I need for invoicing. I can tag any recorded time as billable or not billable and even enter the dollar amount.
I tag entries for specific clients or types of work with various colors which helps differentiate entries.
The weekly emailed report helps me make sure my time is on point.

I didn't find the Windows desktop tool all that helpful, I just use the web interface.
It's not as streamlined to create a new project or client easily. I have to type a project name (which doesn't exist) then I can create it on the fly, but with no details such as setting the color or client. So I have to go to another part of the interface, track down this new project so I can set the client and color, etc. I wish I could set up all the details about project and client directly from the time-entry page and not have to go around the interface to finish adjusting it.

I don't really care for tracking precise start and stop times separately. Each time I have to stop and start a particular project time, it creates another entry. I prefer a generic single timer that accumulates, rather than a bunch of sub-time-entries like 10:34-10:45, 11:02-11:18, 12:50-1:42. This doesn't do much for me. I just want a single timer that says I worked 3.4 hours or whatever. But this is pretty minor thing. I can ignore all the sub-entries for the most part. But where this gets ugly is when I want to come back and enter time manually. If I need to adjust times, it's nearly impossible because I don't want to create time entries that overlap with existing entries. There is a lot of fudging numbers around so I can line up my projects.