Not sure whether it's fair to compare them. Specifications are usually written using a format language for the ones who implement them and not designed to be a learning material, so many things which are not necessary for this goal are omitted. On the other hand references like MDN are dedicated to the end user, written with a regular language and unnecessary details removed but also with additional explanations and usage examples which are really helpful. So one usually doesn't need to refer to the specification unless there are reasons to do it(e.g. need to understand all the aspects of a feature). It's pretty hard to understand what's written there for a beginner without some context which provided by manuals like MDN.

Be sure to read https://tc39.es/ecma262/ instead of the one hosted on ecma-international.org that has up to a year's worth of unfixed bugs.