It's worth noting that libsass's source map support is still ironing out bugs (i.e. https://github.com/sass/libsass/pull/1463), though it seems that the compilation itself is relatively solid. My team finds that the time saved in compilation for a Flask app is worth source maps sometimes not working. Your mileage may vary, though.
libsass is - understandably - a few versions behind the Ruby implementation. Most of the project teams I've been on working with Sass have opted for the Ruby implementation as a consequence.
The ruby version is on feature freeze until libsass catches up.
citation now I'm on desktop:
> In fact, Ruby Sass will not release any new features until LibSass catches up. Once it does, there will be feature parity between the two moving forward. Soon, we’ll have the blazing speed of LibSass with all the features of Ruby Sass!
Just FYI: Neither Sass nor Less should be written in all-caps. See the respective websites.