Which CSS preprocessor should I use?

Hi everybody! I am going to start a project which is basically a community forum web UI developed by React, and I was planning to use a CSS preprocessor to simplify my css work, I have never use this kind of technology before and there are so many options, so guys which CSS preprocessor do you use? And what's the advantage of that one?

Plus. I am going to use ant design (React component library), any recommendation about other component lib ?

Really appreciate it!