It depends.

MDN has a better overall information and is more in depth. And more up-to-date.

On the other hand, w3schools has that one three-line CSS snippet that you need to copy-paste to center your DIV vertically or whatever, without 5 paragraphs of intro.

MDN is much more complicated. I almost always get my answer faster and easier to understand with w3schools. Plus quick little things like browser support and try it (which mdn also has now)

MDN is generally too technical.

As it should be. It's a resource for professional developers, not people who are learning how to code for the first time.

Professional developers enjoy simple and concise explanations just as much as people who are coding for the first time.