If I'd only use a laptop occasionally I'd also use the Hadley (in fact, I do) but if you have to carry a laptop everywhere (plus books and all kinds of other stuff) I'd consider a 335. It fits the 13" MB / MBA perfectly either in the main or front compartment.
If you can live with a different brand maybe check out Crumpler. Ugly and a little over the top, but so much more practical.