Which pro are you considering? The base Pro with the i5, 4 GB RAM, Optical drive, 500 GB HDD? or the Retina Pros?
Is this going to be your main computer or do you have another computer with more power for heavier tasks?
There are much better options for the price you're willing to pay for an apple, but if you're for sure set on apple then if its going to be your main computer get the MacBook Pro. The Base model has a decently powered i5, and it has more internal storage compared to the other models if you want to download your music and movies instead of streaming. Otherwise the retina macbook pros have a really nice screen, have the newer more efficient i5s and have 8 GB of RAM, downside is they only come with 128 GB flash to start with.
If you have a desktop or another more powerful computer to do work on then get the Macbook air. I am actually typing this out on my 13" MacBook air. Its light, easy to carry around, decent battery life, decent screen resolution (the 13" is 1440x900), while storage is a bit on the low side (128 GB and I like to download some movies, legally) its still more than enough. But if I ever need to do things like gaming, converting video and etc, I'll always have my desktop. Would not really recommend a MacBook Air as a main computer.