My experience has been starting with LESS. I built a personal project, then a production project, with what I'd call limited success.
I'm about to start a new project for a large organization and I've decided to use Sass. This is my short list of why I'm using Sass over LESS:
- Debugging. Using most of the Sass compiling tools, you can have the output file list the line numbers and file of the original declaration. I found LESS hard to debug once I hit 2k lines of the compiled file.
- Control Directives. I'm not sure why if, for, and while statements are excluded from LESS, but I'd like these functions available for use if I want them.
- @extend. I like the ability to not have one declaration declared over and over in a compiled CSS file. One thing I've seen, especially in [Twitter Bootstrap](Twitter Bootstrap), is the repeating of declarations at compile time.
- It's how my mind works. I consider myself 30% designer and 70% developer. LESS appears to be more geared towards developery types, while LESS to designers. LESS is to the point, while Sass is a more rounded CSS extension.