Atom is built on Electron -- So is VSCode

GitHub integration is done very well -- Not nearly as well as the Git integration in VSCode

Also, Atom has in the past been much slower than VSCode in nearly every aspect.

VSCode has a built-in debugger which takes it dangerously close to being called a full-fledged IDE rather than just a text editor with plugins cough Atom cough

The reason they keep getting compared is really simple: they both aim to achieve the same goals, and both use a very similar approach.

One editor I haven't seen mentioned in a LONG while, though, that can probably be considered the 'grandfather' of both of these is Brackets. If I remember right, it had a lot of performance issues, as well.