Is this for student use?
The 13 inch Apple Macbook is great, but a bit expensive. Dell's inspirons are bigger and more brittle, but you can't beat the price. While not as cheap, HPs are a bit more rugged than Dells.
If you have basic student needs, I think you'd be happiest with an Apple Macbook. One thing you should know about Macbooks, however, is that in order to connect the laptop to another monitor or projector, such as when giving a presentation, you have to bring an adapter with you (sold separately I think, but not sure).
If you have something against Apple computers (which I don't understand, but is very common), then I'd say get an HP. Dell's consumer grade laptop (Inspiron line) is made out of cheap plastic with poor build quality. I owned one and had the chassis twist and crack in my backpack (Dell backpack designed for the machine). HP's new chassis is quite stiff and tight, exactly what you want and will last in suitcases, backpacks, etc.
Whatever you do, stay away from Sony. Overpriced and not even that great.