illawarra to fraser island what is the best way

can't help with the first part of the question....if you come through Brisbane from the coastal run, the Gateway Bridge toll rd skirts around the city and is a much quicker option (so long as there hasn't been an accident on it that is). you'll drive up from the Gold Coast on the highway, it becomes the freeway that heads into the city, then you take an exit for the Gateway and bypass the city completely. you'll cross over the Gateway Bridge where you'll eventually join onto the highway heading North for Gympie (there's an exit you'll need to take at Sandgate that hooks onto the highway heading North)...with not a traffic light to be encountered along the way.

If twas I...I would go coastal...To make the trip in two days I think is a bit hopeful.

Inland, you might be best to take the New England...But it's a big hop before you start heading north :)

Six of one...I would turn off on the Picton Rd or Heathcote Rd, to get west of Sydney. Then turn on the GPS and go with "toll free"...Or depending on your start point, you might even consider Macquarie up the Illawarra to the Hume.

If it is of any help, I would go up the F6 and turn off (left) on Heathcote Rd. I would not take the "new" right turn, but rather continue through to Liverpool. I would then turn on my GPS and set it for toll free to Fraser...Sydney is really the only issue. But there is an almost direct route from Liverpool to the northern freeway (with a few turns) that is easy and toll free and your GPS should be able to guide you through it.

From someone who lives on the New England Highway, go the coastal route if you just want to get to Rainbow Beach the quickest way.
Nothing wrong with the New England, only about 50km longer and time longer.
When the Hunter Freeway to Singleton is finished though early next year, time wise in a car it will be very close (distance wise still longer), that is until all the Pacific Highway works are completed, then the Pacific will be the quickest again without a doubt.