Macbook Air or MacBook Pro for Medical student?

I have MacBook Pro 13" Mid 2010,Because of my Job on hospital and i study Medicine, I want buy New Apple mac which is more Comfortable ,Portable.
, My working with laptop : Web browsing,Skype, Word,Powerpoint,excel, Read my reference (format : CHM, PDF,...).
Which one is better for me??? It is important to add : now, i live in iran, i want buy new Macbook pro OR air for long years, i can't change it within 4 years. Our Country's Economy Don't allow us to buy new macbook every years.

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