Luke, without knowing you personally, I would only give general advice here. The club you choose should give you the opportunity to play at the top level in your age group. In simple terms, if you are Under 16's and the club only had a team in B Grade or A Reserve, I would look to one that fields a team in A Grade. Also don't be afraid of joining a club which you know has better players than you. Sometimes this scares juniors but I think it is better for you. You learn more from playing and training with better players rather than being the best of a bunch of average players.
Without knowing the set-up directly in NSW, does your friend get to regularly play against Sydney based teams? I say this as the strongest clubs and players will still generally be based out of Sydney. Central Coast and Newcastle, whilst strong, will not be able to consistently give you the high quality of competition than Sydney can.
Good luck with it. Believe in yourself but also ensure you have a back up plan (eg - education). Injuries unfortunately can kill a sporting career so always good to have back up plan.