I'm a huge Air fan.
That being said, if you are going to do Photoshop work, even light work, can you talk to any colleagues doing the same, about their perception of the screens of both the rMBP and the Air?
The Air has a high quality TN screen but may not be as nice as the screen on the rMBP, which has an IPS screen. Of course, the pixel count on the rMBP is much, much higher, but that may or may not be useful for you.
In other respects, they are so close in weight, battery life, etc., you really should focus on what you want to do with it.