Chrome DevTools have the best and most complete offering as well as some really great features. One nice feature that I recently learned about is the ability to diff your live edit CSS changes directly from within DevTools.
Here’s How You Do it
When inspecting styles, click the link to the external stylesheet to open it in the “Sources” tab
Edit & Save Styles
Edit some styles and then save them (ctrl + s)
Navigate to “Sources”, “Local”
Right click within the “Sources” tab content area and select “Local Modifications”
This will open the history panel where you can diff your edits