Both Poly U and City U can provide very good PhD graduates who can publish their work in top tier journal. City U has Kwok Leung. However, you must talk with the PhD students in those universities. To my understanding, the life of PhD students is ........very poor. Kwok Leung is a tough person, not easy to allow you to graduate.
hey, the scholarship depends on the cost of your living there, because the cost varies in different location. So the remaining is almost the same for different schools. My suggession is you need to check the research ranking of them to choose schools.
If I were you, I would choose City U and asked Kwok Leung to be my supervisor later. Kevin Au and Jessica Kwok were under supervision of Kwok Leung and they were now associate professors and got many research awards at CUHK.