The Macbook Air is faster (60% faster CPU and about 15% faster GPU) and has an SSD. The Macbook Pro does have the benefit of the larger screen but the resolution is 1280x800 vs the 11" at 1366x768 so you get roughly the same workspace on both. You can upgrade the storage and RAM on the MB but if they are enough already, it's not a big deal.
I'd personally say the Air is the better option and it will also be worth more so if you wanted to upgrade to a Haswell model or even a Retina 13" MBP when they eventually arrive, you'll get more to put towards it. I have a feeling they'll get the 2013 rMBP down to $1299 and you'd get about $750 for the Air. That leaves a $550 gap but if you're lucky, they might have refurbs within a couple of months at say 15% discount leaving a $350 upgrade.