Ranked in these QuestionsQuestion Ranking
Pro Simple, streamlined GUI
GitHub Desktop uses an extremely simplistic two-panel view. It's not capable of complex historical visualisations like other GUIs, but it is very easy to use (especially for git novices).
Pro Supports pull requests
In addition to being able to seamlessly and easily integrate with all of GitHub's features, it also supports forking and submitting pull requests on any open source project hosted on GitHub.
Pro Great GitHub integration
This is the official GitHub desktop client built by the GitHub team.
Can't handle complex tasks. The Help Manual advises to use command-line Git instead.
Con Incomplete feature set
For e.g. Cannot do re-base, cherry-pick, commit chunks, stash.
Con Non-GitHub repositories are not fully supported
Since this is mainly a GitHub client, other repositories are not fully supported and with as many features and setting up a repo hosted anywhere else but GitHub is troublesome.
Con Not free/libre
This application is proprietary, and thus cannot be modified or freely distributed.
Poster child for authors' programming ideology (FRP), likely the cause for the odd quirks and bugs it has.
Con No Linux support
There's no Linux version of this client.
Con Does not support multiple Remotes for a repo
Only allowed to assign one URL as remote. To manage/sync/fetch other remotes, use command-line Git instead.