You can use your HSBC HK debit card in other banks' ATMs, but usually you will be charged a $30 - or so - fee per transaction. I suppose it depends on what setup you get with HSBC. Unfortunately they haven't got a strong consumer watchdog here (compared to UK) to cry foul at these horrid charges...
Hence the way to go is with the bank with the most ATMs dotted around town, thus minimising the chances of you having to fork out a fee to get to your beer money. HSBC it is then - the lesser evil.