Mate, you're a bit muddled up. All Army officers go through Duntroon, regardless of whether they attend ADFA or not. The only difference is those who go straight to Duntroon (Direct Entry) do 18 months of training at RMC, while those that come from ADFA will only do 12 months at RMC (they do the equivalent of the first six months of training during their three years at ADFA).
Any talk of ADFA grads being 'looked down on' is a load of tosh. By the time you are six months out of training no one will care less whether you attended ADFA or not. I doubt most soldiers would even really know the difference, let alone care. As long as you are competent, your soldiers will hold you in high regard.
The only real decision you need to make is whether you want a degree or not. If you want to make the Army a career, you will need a degree or you won't be competitive past captain. If you want a degree, you might as well go to ADFA and get a free degree, while being paid (its about $45 000 a year these days). The only real reason not to go to ADFA is if you want the whole liberal civilian university experience instead of the more structured environment as ADFA.
The more important decision you need to make though is about corps - the cavalry is far superior to the infantry...