Second that about St John's. Great if you're outgoing and extroverted. The culture is that you pretty much are expected to spend a lot of time on hall activities. For people I know who lived there, the challenge was getting enough balance to give academic work the focus needed. Not so good if you need more down time or want more balance between hall related stuff and general HK life stuff.
Check out the individual hall rules - overnight guests, opposite sex guests (ok in own room or just in public areas?), alcohol, general facilities etc. Own room or sharing and if so with how many others? Sharing a room or do you have your own room in a suite with shared facilities? The guest and alcohol rules tend to represent the biggest mental adjustment for many non-Asian international students.
BTW, if you're sharing a bed-room, note that many local students may not be comfortable with you bringing back overnight guests, and may not have somewhere they can sleep over if you want privacy. This can be a change from people used to US style dorm culture where either the room-mate deals with overnight guests in the shared bedroom, or goes somewhere else for the night.