This is an old question, and the answer depends on what you really want (and need) from the computer.
If portability is the main consideration, then the MBA is the answer. I have a 13" MBA and it is easily the best computer I have ever had. Plusses: the portability - it is brilliant for travelling and working on the move. The SSD is also fantastic (I had a HDD failure on my MBP), blazingly fast and wonderfully stable. And, until the advent of the retina screen, the screen of the MBA knocked the socks off almost everything else.
Minuses: well, it is not as powerful as others in the Apple lineup, and certainly not as capacious, as the SSD (unless one is prepared to pay stratospheric sums of money) drives (especially as they increase in size) become quite costly; in terms of value for money, HDD offers a lot more.
For now, Pro Retina offers a stunning screen, a somewhat heavier computer, and a battery that is a bit greedier than that of the MBA, and so does not last as long. So, it depends on what you prize, or need, more: Portability, or terrific screen. Your call and the very best of luck with whichever of them you eventually choose to buy.