I would get the Retina.
Although the Air is marginally cheaper (and the difference is smaller if you have an education discount - $100 off the Retina but only $50 off the Air), it is not as high quality - the screen is, of course, not in the same league, and the hardware doesn't feel as refined (this is just a personal preference, though).
The Air is lighter by ~0.6 pounds, but a laptop is not a device that you use while holding it in the air (like you would with an iPad or an iPhone). The weight difference will only matter when transporting it, and you won't really notice that difference (or it won't matter).