Once you've tried a retina screen on a laptop you won't want anything else. I've both the 13 and 15" retina mbp and they are delightful. The 15 is great for 1-on-1 presentation because the screen is large and beautiful. The speakers are great for a laptop. But it's really heavy and the 13 will last a bit longer off the charger. I don't need the discrete graphics card of the 15".
The MBA is lighter and the battery life can't be beat. But the design is ugly with a thick silver frame around the screen and that pointless wedge shape. If you can wait wait for the 12" retina MBA.