MacBook Air 13" vs. MacBook Pro 13"

I'm thinking of switching to mac, and since I'm student I need a good laptop. I'm choosing between MacBook Air 13" i5 with 4GB of RAM and 128 GB SSD and MacBook Pro 13" i5 with 4 GB of RAM and 500 GB HDD. So which should I get Air or Pro, or should I wait for the rumored MacBook Pro 13 with Retina Display and get iPad now? My old PC is almost dead, and I need something for Surfing Web, e-mail, iTunes, Movies, and most important Documents and Notes. Is 128 GB enough, and is the Pro too heavy?