While evaluating the Flutter and Dart plugins recently, I found the following for each which maybe worth mentioning:
The quick documentation can be set as a nice standalone side window.
The quick documentation has an option to adjust font size more easily.
The syntax highlight seems to be better in the quick documentation in VSCode than IntelliIDEA Ultimate, for example, if the document has some code snippets, VSCode will also use syntax highlight. In IntellijIDEA it remains plain black text. And VSCode's quick documentation seems to be more well formatted as well.
The quick documentation can remember the position I read last time in the same file session. For example, if I move my mouse cursor to a SDK class, the quick documentation pops up and I scroll down as I read. Next time when I move my cursor to the same SDK class (not necessary the same position in the file), the popup will show again and keep the same scroll position I read last time.
It would be nice for IntellijIDEA to have features like VS Code.