Also, the mouse will generally beat the keyboard for selection tasks, which is a decent amount of git usage. Splitting up changes in your working directory into multiple commits is substantially faster with a GUI, as well as a lot of commit graph manipulation options.
A couple other things the CLI sucks at:
- Complicated staging of chunks of files - Complicated interactive rebase
For some operations it's more that one command, so you are present with more than one dialog.
For me it's not just a convenience, but a learning tool about more obscure Git operations and their parameters. Several times when I found the documentation obscure I would just make Git Extensions generate a command, and it helped me to understand a command -- or discover one.
Having said that, I find Git command-line interface hard to memorize and not very consistent/logical, so I prefer to use the GUI when possible. And you cannot beat it for partial commits or resets.
I also recommend against using git GUI for beginners just because it hides so much of what's going on, making it easy for people to stop learning after they figure out how to do exactly 2 things with it: commit and push.
But honestly if we're going for "best" I think magit is the winner.