The two most important factors of a blade are its size and its material. Firstly, consider the legality in your local area. For example, the blade size is limited to 2.5’’ in Chicago. Blade size ranges from small (anything under 2.75’’), medium (from 2.75’’ to 4’’), to large (anything above 4’’). Small blades are lighter and simpler to carry and usually legal in most places. The medium size is perfect for everyday carry. It suits both detailed cuts and heavy chores. The large knives can handle tasks as well as fixed blades but can be folded for easier carry. Secondly, the material is significant. There are stainless steel and high carbon ones. Also, another huge factor is the heat treatment of the steel, although this information is not generally shown on the spec sheet. The type of steel and how it is treated results in different toughness, edge retention, and sharpening, so make sure you get the alloy name of the knife, such as 440C or 8Cr13MoV.