My bet is on the T6, simply cause it's cheaper - which is a crying shame and hardly an improvement on the PC9 - in some areas, less capable.
The RSAF allegedly approached the RAAF during their lead up to the acquisition of their PC21s and said something along the lines of "Hey, RAAFies, how about we buy a shed-load of PC21s for a good price and have one maintenance base at Pearce and a couple of sims - makes sense, huh?" And the RAAFies said, "Um, we need to take the requisite 15 YEARS to come up with an answer - can you wait for us?" No kidding, the PC9 replacement project has been in the works for just on 15 years - numerous "project teams" have all had their go on the project, spent countless hours researching, handed over to their replacements (corporate knowledge lost along the way...) and the result has been a big fat zero. I'm surprised Raytheon or Pilatus can even be bothered with us anymore. Bananas...