I started using Less for a new project. It worked great until a new version came out with some nice new features that I immediatly used, but also with a bug where it replaced all the plus signs in my base64 data strings with spaces, totally breaking them. Since then I've been doing line by line commits to get around the problem, but hopefully it gets fixed soon!

Could someone who has used LESS and SASS compare the two?

You can do all the important things that Sass can do, but with the added benefit that CSS is also valid Less.