If you have no reason to believe that you need to use Python-based, I would recommend that you use the best tool to work. I don’t really like how LESS and SASS use Ruby & mdash, I would prefer Python & mdash, but if that's what they use, then what they use and I'm not going to complain too bitterly. I would use only the worst, such as CleverCSS, in favor of the excellent one if I needed to use it from Python code, and the performance difference was quite significant compared to running the script. And this is a much less common problem.
As for options, I think Stylus is the best available; in different things, this is better than LESS and SASS (not least its transparent functions / mixin calls & mdash, so you can have, for example, a border-radius mix that will accept valid CSS border-radius: 2px; and add to him any prefixes that you feel). And this is written in Javascript, not Ruby, which is positive :-)