I lean toward the 13" Air. My current work laptop is a 15" Macbook Pro, but I have an Air at home. If you don't need the larger screen, which I don't because I plug into at least one extra monitor most of the time, the Air is a nicer package. Less to lug to and from work. The other caveat is that, if you need to run multiple development virtual machines for testing, the 4GB memory max for the Air is somewhat limiting.