Sydney Boys by far overall. Not just biased either. Except for the odd talented athletes from surrounding schools (South Sydney would probably rape them at rugby, if they played the 15 man game), they dominate pretty hard. I remember one year in cross country in my age group we got the first 9 out of 10. The guy who came second, Ali, moved to our school the next year
BTW, not sure if it's changed since but before the only things we did in CHS were sailing, rowing, athletics and cross country. We used to pwn grafton at rowing.