If you are looking at them new it is hard not to get the 27" Retina. With the added specs and included fusion drive (which I consider a must anyways) it is barely more expensive than the non-retina.Thanks. I've been offered a late 2013 iMac with 32 gig ram, 3.5ghz i7 for about $2500 Australian. To spec up the retina iMac will be about $3500 to $4000. thinking the 2013 could be a good move for now.
Different if you can get a good deal on a slightly used one and I don't know how prices are outside of the US.