This is an interesting question. As far as a general sense, the machine is an absolute beast. The screen, the performance, the form factor, the portability, everything about it is awesome. I have been using mine for a few months now and it is by far the best computer I have ever owned. But the question for you is what are you computing needs? Are you a video editor? photographer? hardcore gamer? Web Developer? If so, then this is the machine for you. If your a casual browser, light email usage, basic needs person, then the MacBoor Air is much better suited for that due to the price tag. Those are my opinions on this.
Unless you really need the 15" screen, plan to use it for video editing, 3D modeling, or gaming, I'd go for the 13" MBPr. Otherwise the graphics card really isn't worth the extra expense since the machine will probably be using integrated graphics the whole time.