The best school is the one that has the instructor that you get on well with. Do the leg work and meet some.
I would suggest that once you've ticked the IREX box, the best learning is in the air or by yourself developing wx forecast reading skills and becoming very, very familiar with the charts and the GPS you will fly. Practice with an online simulator.
Right now; I'd decide if you are going to go the AsA route or Jepp route and whether you will go paper or iPad. The training you do will entrench this choice. If you go iPad, then get sorted with battery backup, external bluetooth GPS unit, kneepad / holders, etc. Choose your program and become fluent with it. IMHO Avplan is a better IFR program than OZrunways, but I prefer Jepp charts, so I have Avplan for flight planning & Jeppview for flying procedures. There is no good reason for this. Its just what I like. In flight Jeppesen Flitedeck is best, but it needs a windows based tablet and it all becomes harder than iPads (I carry a dedicated mini plus my day to day big one as backup).
There are less school / instructor options now under the new part 61 licence rules. Some of the best guys have not bothered to maintain their test officer status and others have effectively "closed their books" and are not taking new students. Thanks CASA. Another step forward.
This is especially so if you need to hire a twin. If you don't have a twin endorsement or limited twin time, remember that the aircraft type you do the MECIR rating in will be the easiest aircraft type to hire / be insured in. Its best to do the training in an aircraft type you will fly.
In alphabetic order; start by visiting Bini, MFS & Vortex.