After a horrible experience with Booking.com and a dodgy hostel calls Day and Night at Chungking Mansion Building (literally a pigsty) I have just stayed there for one hour and then I found The Mahjong and everything was totally different, clean, tidy, neat, friendly staff and comfortable place to stay. No doubts the best Hostel in Hong Kong (They also have inside the premises a lot of certificated, and you understand why)