To provide a counter-point to jwcooper, I've used both the original LESS and the SCSS version, and I have run into a couple of minor quirks (things like elements inside input groups not lining up correctly) with the latter.
While I've always personally preferred SCSS over LESS, when I'm starting new projects these days I tend to just use the LESS version of Bootstrap, as it makes it much easier to update, it's tested much more widely, and fixes for any issues that do crop up are available faster.
Sigh...I'll probably have to do it in LESS as well. Do you have any tips on good typography mixins for LESS, if any? I'd miss Compass and Typeplate very much if I end up switching. Thanks to everyone that replied btw.
Ooh, I hadn't seen Typeplate. Thanks for the tip :).
I'm not aware of any LESS equivalents (but then again, I do very little LESS work).
It may be heresy, but I haven't had any issues using both preprocessors in a single project, so I'll often just use LESS for Bootstrap-related stuff and SCSS for everything else.
as I understand it, bootstrap-sass is going to become the official SCSS version of Bootstrap, and as such bugs on bootstrap-sass will be considered bugs on bootstrap itself.
While I've always personally preferred SCSS over LESS, when I'm starting new projects these days I tend to just use the LESS version of Bootstrap, as it makes it much easier to update, it's tested much more widely, and fixes for any issues that do crop up are available faster.