Well, if the hinge and on the new MBA is as sturdy as the old one, then I would definitely prefer it over the 12" MB, which feels flimsy and is less powerful.
So OK, the MBA has the same footprint and screen as the 13" MBP, but it is a little lighter and - perhaps most importantly - it has a claimed 12 hours of battery life, which is two hours more than anything else.
And that alone is why I would consider an MBA over the others.
It was that combination of light weight and battery life that attracted me (and I suspect others) to the MBA to begin with. My wife replaced her old 13" MBA with a 13" nTB and has regretted it ever since. The keyboard obviously has a lot to do with that . . .