iMac 21" 2012 vs iMac 27" early 2012

[-BigMac-]

Hi Guys.

I have a rMBP, iPad, iPhone 5. among many other things in my room.

I want a permanent desktop sitting on my desk when a mate is over and im on my rMBP or iPad or when i want to do some photoshop (ridiculously light). i know. i have money to spare - but not to waste.

I dont care about..

- graphics
- processing power
- weight of product

I care about..

- harddrive options. it NEEDS an ssd.
- the best option. based on money/performance.
- who doesnt like a bigger screen when affordable

Is it worth possibly even getting a 2010 27" or even an old 21"?

will take mad pics of room once this baby has been bought

Thanks