But don't lose hope! I'm not really
that much of a frequent flyer, but I have had my fair share of harbour views.
That said, get a better camera than me. An iPhone 5 just doesn't cut it.
Just for some perspective, this was just a few minutes before landing, approaching from the northeast. This was from an A seat, looking more or less southeast. As you can see, the plane was passing well north of the harbour (don't recall ever flying south of it on arrival), so I'd definitely suggest going for the A seats.
On departure, sometimes the planes make a right turn immediately after take off, in which case you may pass across the western entrance/exit to the harbour, and that can be quite a decent view as well. That would again require an A seat. But if passing over the harbour, then probably the K seats would be better.