what all should i consider while buying a baby bag/diaper bag?

It has to be spacious, light and the design has to be nice. Ju Ju Be is very popular with mothers because it has many compartments and is relatively light and stylish. However, it is rather expensive. Currently, I'm using a waterproof backpack with a few compartments which I purchased from a store in the nearby mall. The Anello backpack is also gaining popularity. It wasn't designed as a diaper bag, but is very roomy so many mothers are using it to store their baby's essentials. http://list.qoo10.sg/item/BUY-2-FREE-SHIPPING-READY-STOCK/436566460