Transit visa to Hong Kong International Airport.

I have a conference in Guangzhou, China for a week and will fly back next April 2019 from Hongkong International Airport to Berlin. Do I need a Hong Kong entry permit to get to the Hong Kong international Airport? Is it better to take train or flight from Guangzhou to Hong Kong? I heard that if i take a ferry from Shenzhen Shekou to Hong Kong Airport, is it not needed a Hong kong visa. Please help me to clarify it. Thank you very much!