I don't have Citi but a mate (I say this because he's Australian) uses Citi. He says that it's alright.
SC priority - I like the credit card (for air miles) & the fact that there aren't many people that use SC so you never have to line up - however there are fewer branches. Internet banking is alright - it is easy. Service is alright. Able to easily set up accounts in other countries when you need.
HSBC Premier - crappy credit cards, good number of branches but often in Admiralty you need to wait 20 minutes. Really poor service, terrible internet banking interface, high IPO interest margin costs, and lots of red tape if you want to set up an account in another country.