Actually I much prefer GC North for plane spotting and lounge experience too. GC South becomes incredibly busy at certain times of the day that you can't even find a seat, in general it's difficult to find a seat next to the window. If you go to GC North I'd suggest the seats at the end of the lounge, near the small business area, because in my experience it's quieter. The GC Terrace is another great place I like to spend my time, though not always it's good for spotting.