13" MacBook Pro vs. 13" MacBook Air?

So my early 2009 white Macbook is on its way out, hanging and slowing down and generally being troublesome. Consequently I am looking to replace it with either a 13" MacBook Pro or the same sized Air. I would like the forum's thoughts on which one is the better choice.

Specifically I would be getting the Pro with the 2.5GHz processor, 500GB HDD and 8GB RAM, or the 13" Air with the 1.8GHz processor, 128GB SSD and 8GB RAM. The prices are approximately the same.

I am just finishing a PhD in the UK and will be using this alongside my iMac for the next few months, and then I will be moving to Nepal in January, where the new laptop will be my sole computer for 9 months or so.