I am working in clinical trial department in a pharma.
Actually the 2 biggest public hospital, Queen Mary and Prince of Wales are very good in terms of oncologists and hardware. A c hing also replied above, public hospital is good because it has many doctors and they exchange and review data together. Queen Mary and Prince of Wales also have private sector. Some Professors and Associate Professors can take care of you in "private settings". Of coz, fees and drug fees will be similar to private oncologist (consultation fees are similar but drug fees MAYBE lower).
if you go for private hospital/clinic, I think Sanatorium has a doctor who is specialized in renal (kidney) cancer. I forgot his name but you can search their homepage. Otherwise, Hong Kong Intergrated Oncology Centre also have several famous oncologists.