I think you should think on your needs only.
I got the '11 because I travel a lot, and needed mobility. When you are on a plane '11 is the perfect size, for example.
The '11 is ultralight. You get 5 hours battery and I've never had problems with power. My girlfriend bought a '11 too, she couldn't decide between '13 and '11 but I convinced her. She is really happy with her notebook now, because it fits in her purse (She bought a cover of course).
On the specs side, if you are not doing imaging and video editing, I don't think you should even look at the specs. The macbook air is a very powerful machine. If you are doing any other work, it will be fast enough.
On the screen. You won't even notice after 1 day. And it's really beautiful. I watch movies, do Excels, words, browse, facebook, do little gaming etc. I don't miss the extra real state. I think that for coding and image editing it is small.
OSX is ultra efficient too. Your computer will last at least some 3 years. I got the 2011 model and I was really looking for a reason to buy a 2012, but just couldn't justify it.
My '11 is a 4 gb ram, i5, 128 gb ssd macbook air.
Hope it helps!