prelude-ls really shines when combined with LiveScript - syntactic support for partial application, currying, function composition, "pipelining" (|>), implicit arguments and so much more really make a difference.
That being said, I'm very interested in mori, immutable-js or lz.js. prelude-ls is nice, but is designed to work with native JS types and provides no extended semantics that I'd find useful. It's still my go-to library when working on the frontend and it probably will remain one, but I'm thinking about contributing some support for other advanced collection types to it.
I started writing a comparison between un-sugared JS and LS use for functional programming patterns, here: https://klibert.pl/warsawjs-talk/code.html (for the talk I gave: https://klibert.pl/warsawjs-talk/).
That being said, I'm very interested in mori, immutable-js or lz.js. prelude-ls is nice, but is designed to work with native JS types and provides no extended semantics that I'd find useful. It's still my go-to library when working on the frontend and it probably will remain one, but I'm thinking about contributing some support for other advanced collection types to it.