If you haven't been to Sydney before - definitely the IC at Circular Quay. The one at Double Bay is very nice and in a lovely suburb but to get to the main sights you will have to travel into the city - although if you take the ferry that is a very pleasant experience - limited schedule I think during the day.
At the IC Circular Quay try to get a Harbour View room preferably with Club access - club is included if you book through Virtuoso.