I just stayed in the Renaissance. I didn't even see the Marriott, but I thought that the Renaissance was plenty convenient. It is literally 1 block from Circular Quay station, which means convenient to ferries to the zoo (don't miss it on a nice day), Darling Harbour, and the Captain Cook coffee cruise. It's also close to The Rocks and doesn't cost AU$400/night like the Hyatt. I thought it was very nice, and the service was excellent.