In this podcast, I had a chat with a local student on using cash or card. 
He said he's more used to using cash. Also, using cash can help him keep count of how much he had spent. 
He added that using an oyster card is the best way to hop around in this country. 
Daily cap is non-existent in Hong Kong but here in the UK, you get your fare automatically capped after a certain amount. You can then make as many journeys as you like from then on. It's a good idea!
He ended up saying "using cash is a good way for socialising". How so? Listen to this podcast and find out more. 

@foonology