That is what I was wondering... iMac 2013 21" or iMac 2012 27". What would you recommend?
No brainer. Get the low end 27" at the least.
You get bigger screen
You get 7200 rpm HDD (yes it matters)
You get a bit better GPU
Most importantly?
You get accesible RAM door which is upgradeable by yourself, which also saves you tons money if you want to upgrade to 16 or 32 GB.
So really, there's only a few reason to get the high end 21.5" instead of the base 27".