Hong Kong is not really a city state, but more comparable to a conurbation such as greater london, west midlands, greater manchester as there is more greenry (according to the maps) than urban areas, around 65% to 70% of Hong Kong is still rural.
there are always going to be advantages and disadvantages between Hong kong vs greater london, west midlands and greater manchester, it really depends what suits your needs, at the current moment, HK is better for me and my family lifestyle due to lower direct taxation, better public transportation, less crime and less likeliness of economic threats such as brexit or recession