The "best" is probably not free. This one doesn't need Kontakt and it is not really cheap, since it covers "only one" instrument, but it covers it in all facets:
https://www.spectrasonics.net/products/trilian.php

Here is a video of a product presentation and on my wishlist ever since I've seen it:
https://www.youtube.com/watch?v=dsj26oEoBfo&index=8&list=PL3D640C9CAF78418C

There are many videos on YouTube covering the possibilities of Trilian.


Desktop; i7-2600k, 8 GB mem., Win 10 Pro, BIAB 2017; RB 2017 - latest build
Laptop: i5-2410M, 4 GB mem, Win 10 Pro, BIAB 2017; RB 2017 - latest build