Egghead.io has a range of good JS courses but the following are really great courses about React and Redux. React itself is the most declarative way of programming in JS that you are going to find. Redux is a great framework and the egghead courses about it are easy and teach you a lot of functional (and declarative) design patterns.
I guess only more bias :D confusing frameworks with language design :) but still it's fun to read :)
Jon
ClojureScript Developer.
Seriously, I would say http://clojurescript.org/
JavaScript is an imperative language, there is always troubles trying to write it in another way. So to satisfy the word "best", please try another language.