South is slightly less touristic, but in that period you will find a real desert
you may have problems finding restaurants open, so don't worry about crowd
Both are stunning places. If you love waves, south is better, and also more wild than north
however, in the north you can have a daily trip to bonifacio (amazing!!) and also tour around the archipelago of Maddalena, with fantastic islands and beaches
you can't go wrong with any place!