When I sell a customer a computer, as soon as "light graphic design" is tossed into the conversation, I automatically try to steer them away from the Air. Just a bit too underpowered, even for the lighter design apps.
Go with the Pro. It will be worth the additional cost down the road. Spending a couple hundred extra will be well worth it. Opt for the 16GB RAM, but the 128 SSD will likely be fine, considering you can get some pretty solid external storage these days.
Boise State! … Boise State! … Boise State!