I was a die-hard ST3 user. I looked at Atom and it was slow and sluggish at the time. I gave VSCode a try after it added support for restoring unsaved changes (i.e. being able to edit a file, close and reopen VSCode and not losing your unsaved changes).

The biggest advantage of VSCode over ST3 is its code intelligence. It's the kind of quality you'd expect from an IDE like WebStorm/IntelliJ but without the entire weight these IDEs usually bring to the table. VSCode still feels genuinely "fast enough". And if you work with JavaScript, the code intelligence even becomes better if you have dependencies that have community-provided TypeScript typings -- you don't even need to use TS to benefit from the built-in TS support.

Other than that, the extension ecosystem is very strong. I missed a few ST features initially (mostly specific keyboard shortcuts) but there are extensions that provide all of that (including an ST keymap) and more. It's also fairly easy to write an extension yourself if you know a little JS.

For me, the most awesome part is the debugging experience out of the box. If you're programming for NodeJs (or other supported languages, with a bit of configuration), you can click on the side to add a breakpoint and hit F5 to run, step over your code and hover variable names to see what they hold, evaluate expressions to change things and stuff like that. Still in the JS world, VS Code uses the TypeScript engine to infer variable types and detect type errors, which by itself catches a lot of bugs.

These features aren't unique to the JS language though. Extentions do have access to the APIs that implement these features, so you already have them available for most languages (with different levels of quality/completeness).