The capacity and storage depend on person to person. Some people rely on the bigger capacity while some rely on smaller and compact designs. At the end of the day, it depends on you and the kind of requirements that you have. If you are travelling all the time, get one with more capacity. If you are just carrying your laptop, it is okay to get smaller ones. You should get a laptop bag based on the size of the laptop you have. You have to make sure that it has enough space to accommodate your entire laptop.