Ah the classic 13" air vs 13" pro debate. I was in your same shoes earlier this year and opted for the air. Heres why:
The air has a higher resolution screen: 1440x900 compared to 1280x800 for the Pro. I appreciate those extra pixels alot.
Lighter: With the latest iMac update, Apple has eliminated the optical disc drive from all it's consumer products and the retina MBP's. Do you know why? No one uses them anymore and it adds weight. You'll hardly notice carrying the air in your backpack but you will notice the MBP in your bag.
SSD: The air comes with an SSD that makes the computer a lot quicker for certain tasks (notably booting and launching apps). You wont see the app icon bounce once before the app opens.
Now obviously there are reasons to get the MBP. The CPU is more powerful (if you absolutely need it, depending on the work you do with it), and because they come with standard hard drives, there is more space available. Also if you absolutely need the optical drive, then the MBP is your choice.
My recommendation, if you do get the air is to upgrade it to 8GB of ram. The airs have next to zero upgradability, the ram is soldered on. I would future proof your air and just get it with 8GB.
