I subscribe to about 4 - 5 online travel agents newsletters (travel.com.au / travelzoo / best flights / expedia etc) and when it comes down to specials they are within $20 of each other, the only difference is often the "speed to market". Best flights usually gets the lead on specials by about 12 - 24 hours (not because they are preferred but they can put the fares online faster), followed by travel.com.au and a few days later with the main street travel agents. Which on real specials can mean the difference between woe and go!
The Australian travel market is so regulated that it is very rare these days to see any agent with an exclusive special that other agents, including online, can't match. travel.com.au won't have a $200 - $500 cheaper special than everyone else for instance on a major carrier. (Yes perhaps on lastminute or distressed inventory but that's getting rarer as well)
Because of the lack of real deal based competition, the last 5 years have seen alot of "mutton dressed as lamb" specials. Which will either be deceiving because of special requirements, hidden taxes or fees (the current best flights MH special) or because its just an everyday airfare via whoop whoop on Dodgy Air with a few dollars off.
The best deals ever are usually airline
1. Launch Deals
2. Anniversary deals
(This is jackpot time, but you have to be vigilant)
The next airline to launch to the US is Delta, keep an eye on their website, sign up for their newsletter. After that will be Jetstar when their 787s arrive.
Good luck and welcome