I have the 13" rMBP (the same one you are looking at refurb - assuming it's late 2013 model?).
I think you are getting a lot more for your money with the rMBP. Better processor, much better screen, better connectivity (HDMI for example). I also prefer the look of the rMBP over the air. For me one of the things I asked myself was "Will I be happy with the lower res screen on the air in a year or two's time?", the answer for me was def no, that made my choice much easier. Plus for work, you can change the resolution to give yourself more screen "real estate" which makes working easier.
Portability wise, the rMBP is still very portable and not much weight difference, prob notice it picking them up with each hand, but in real terms, you will be carrying it around in some sort of bag and not really notice.
The only reason I could see for the Air is the battery life of 12 hours or so. But I get about 8 or so out of my rMBP so it's not exactly bad!
Hope that helps you some! Good luck with whatever you choose!