by Robert Brenstein.
Ubuntu will be better than Windows for sure. 180-200 people taking a quiz at the same time can stress the server to the limit and beyond. The latter will cause crashes and/or freezes. Quizzes put really heavy load on the server. Further, you may not have enough RAM for this. You should study carefully information in the intro of the hardware and performance forum and read many of the threads there. You will likely find all the answers.