Hongkong Visa for Viet student transit in HK

Hi, this is Max.
I am holding Vietnam passport, studying in Australia with Australian visa. Just wondering if I would like to stay in HK for 3-5days as I am take a flight from Sydney, Australia to Ho Chi Minh City, Vietnam via Hong kong as I have friends there to visit, what should I do? I also have been in HK a couples of times years ago. Should I apply for tourist or transit visa?
Cheers,