Should I learn JavaScript with W3Schools or MDN?

Use both, but for different jobs. W3Schools can be a friendlier first explanation when a topic is new. Keep MDN as your reference when you want more complete detail or run into something the simpler explanation does not cover.

MDN can feel dense if you try to read every page top to bottom. Treat it more like a reference: start with the overview and an example, then look deeper when you need the extra details. You do not have to understand every edge case before writing beginner code.

Pick whichever explanation gets you unstuck, then practice the idea in a small JavaScript file. Reading either site without trying the examples can make the material feel more abstract than it is. As your questions get more specific, MDN is a good place to check the fuller explanation.