Top loading means last in first out. So, if you are interested in top-loading, make sure the thing you need at last, you put it at the bottom and the thing you need so often, you put them at the top. Here, know one thing that whatever the thing you are going to put at the top, should not be heavyweight and the things weigh a lot, should be put at the bottom. Remember, your hip should carry more weight than your shoulders.
Front-loading means you don’t need to dig for things lay at the bottom. In this sense, this is a much better option than the top loading system. You may face little difficulty while loading in front just because it won’t open fully.
Though front loading is great for accessing things from the bag you will also find some U-zippered opening that let you access your stuff so easily.