Kraken is the first UI that I've found that makes editing commit messages on previous commits easy. I spend an inordinate amount of time moving hunks between commits/etc in order to present a "clean" git log for a couple opensource projects i work on that have OCD maintainers.

Avoiding the rebase/edit/ammend/etc cycle is a huge time saver. What I really want it to do is be able to select a random hunk and move it as well...

I was on the GK team a few years ago, so I'm obviously biased, but I believe that GK—specifically the design of graph[0]—helped me a lot to level up my git-fu.

[0] which was created before my time at Axosoft, so I'm not that biased :-P

GitKraken is the best git GUI I've had the pleasure of using.

Closed source so it is a no go for any serious projects sadly.