I had the chance to visit both places in the summer of 2013. To be honest when it comes to spectacular views I feel that zhangjiajie trumps yellow mountain. If you do Mt. huangshan plan around three days to include walking up both sides of the mountain and then spending a day walking around at the top. I suggest taking the eastern route (yungu cable car) to go up its not as difficult as the western route (yuping cable car) and the eastern route is shorter. Now can you do this all in one day its possible, but you had better have very strong legs to do that. There are hostels at the top of the mountain they are on the expensive side relative to other chinese hostels something like 150 yuan / night.