I'd suggest QUT, because North Quay better serves that side of the CBD, and the riverwalk is right there. If the city cycle was intergrated with the go card...
You could also argue for South Bank 1+2 as you could run the network with the City Cat forming the line haul route, and use the smaller Cityferries to spread around the city. Would people really complain that much if when their Citycat pulled into North Quay there was a Cityferry sitting there to take them across the river, while the Citycat continued on up/downstream?
RE: Simon's post
I don't see why you want to remove the connection West End/Guyatt Park->Regatta->North Quay/onwards? I can MAYBE understand removing the run from North Quay->Regatta as it's competing with buses on Coro/199/Cityglider, but I still think it's possibly worth keeping. I certainly wouldn't support closing the Regatta.