It’s been a long span of time since I’ve used GitKraken or Atlassian Sourcetree, but GK had some serious performance issues with larger repos in my experience. Very clean app, though, and I did enjoy it.
Right now, Im partial to Sublime Merge[0] as it’s fast, has a clean UI for diffing, shares many similarities with Sublime, and also shows the use what git commands they’re running by hovering. It can be a very effective tool for learning git. It has the same evaluation structure as Sublime, so that’s a bonus as well.