I find plain CSS easy enough to not use any of the mentioned options. Especially with an editor like WeBuilder (not to be confused with Web Builder), with a number of CSS tools built in, writing CSS really is a peace of cake. And I think it is important to get a thorough working knowledge of the CSS syntax. Which gets less if one uses SASS or LESS, I'd think.
I agree that you should learn CSS first then maybe look into SASS. I know a few who love to use SASS and wont go back to CSS. I suppose it depends on the project as I tend to do CSS as I find it quicker personally. But you can write some great semantic code with a preprocessor.
Sass is alot of fun once you start to use some of the more advanced areas of it like mixins. I havo one that makes writing media queries a snap, but I pitty the next guy who has to look at it as it adds it directly to the selector.. meh..