One of the main things you need to establish before you even start looking for the best hiking backpack for your adventures is the carrying capacity you require, which is dictated mainly by how long you travel. Roughly, you need  20-15L bags for single-day hikes, around 30-50L for overnight stays and over 50L for long backpacking expeditions. Where you opt for the top or bottom end of the scale will depend on how light of a packer you are, the time of year you're travelling and what activities you're doing.