There are a myriad of different transport options to get you to and from Sydney Airport. It is awesome when family and/or friends can take us or meet us at the terminal. This arrangement is not always possible, and especially for a frequent flyer. There used to be an airport bus, however the Airport Link train system has replaced this mode of transport. How do you get to Sydney Airport efficiently? Catch the train? Taxi? Drive? Use a shuttle bus service that picks up multiple people on the way? When there is track work on the Airport Line - have you ever used the bus replacement service?
I live on the Airport Line (T2 green line) - therefore the train is fantastic. Only takes me 10-15 minutes. If track work is scheduled, I book a cab. Otherwise I try not to travel interstate for work or pleasure when track work is on. Can use my normal Sydney Trains weekly ticket, and then buy a gate pass for a reduced rate, than if I was to buy a standard ticket.
We live on the northern beaches and I find catching a shuttle most cost effective and simple. They always turn up on time, have plenty of space for luggage and get you to the exact departure gate, so you don't have to carry your suitcases very far.
Now that Uber operates in Sydney, it's possibly the better option if you're not on the train line. The cool thing with Uber is that they charge by distance only, so that can make it cheaper, particularly during peak hour traffic.