My MacBook Pro 15 is heavy – should I get a netbook or a MacBook Air?

I have a macbook pro 15 inch and I really love it. But when I need to go somewhere for the day and have a computer with me, it's a little to heavy and bulky to fit in a backpack. So I explored some options, I could either get a refurbished macbook air or a mini netbook. What do you think?