Alexandros,
are you talking about doing one of those CPL/MECIR/ATPL theory 'all in one' courses or do you already have a CPL and just want ATPL theory?
If you're only after ATPL theory, Disco is right, Len Sales is definately the way to go! Have only done Flight Planning and Performance so far, but he is brilliant!
If you're after a 'all in one' package. You're right, there are plenty of schools in Oz that all advertise this. Some are better than others, but choosing a school is like choosing a car, what suits some, might not suit you. If you can afford to, come to Oz, have a look around at the different schools before you decide where to go, or at least find people who have had experience at these schools.Its a lot of money to spend so do your research. Do a search on this forum for information and opinions on different schools.
Capt Mo