As someone who currently owns the three units in question: 11.6 MBA, 13 MBA, (two) 12 rMBs, along with a 13" MBP that this kids use, I'd say you need to spend some time with both of them. This is highly subjective as YOU are the best person to judge the weight and portability, as well as the quality of the screen. Nobody else can authoritatively tell you which is better, but your own eyes and hands.
Comparing the 13 MBA and 12 rMB:
13 MBA Pros
- Significantly better battery life
- Slightly more power (Whether or not you'll notice depends on what you use it for
- Larger screen, which will be nice if your eyesight isn't great
- More ports (may or may not be important, depending on your plans)
12 rMB
- Lighter and smaller (The difference is enormous, for me, but YMMV)
- Better screen - my eyes are pretty good, and it now pains me to use my MBAs. NOTE - if you crank down the resolution on your rMB, you will effectively have the same desktop as the 13" MBA. It will be smaller, which is bad for some, but it will be much clearer, which is more noticeable to some than others
It's subjective, but to me the rMB feels more like carrying around a tablet than even an ultrabook. Again, I've come from years of MBAs, including the first horrible release.
But one thing is for sure - If your new 13 MBA is one of the ones with only 4GB of RAM, return it and get 8. That's one of the unfair things about these comparisons - they usually compare the lowest end 4/128 MBA with the base rMB which is 8/256. My feeling is that 4GB is barely acceptable today, and will soon be completely unacceptable. 8GB is OK for me, but my desktop sports 32.
I cannot see buying the 12" Macbook and returning the 13" MBA I picked up for $849.
I'm new to the Macs but steer me right if I am wrong. The Macbook will be lighter and better resolution and better battery life. Anything else?
What throws caution into the wind is the processor and graphics, and of course an extra $300 but that was even more till the Macbook went on sale so a better consideration now.
The resolution isn't bothering me on the MBA per se but having better would be nice.