I consider a 6" blade to be a medium size knife and not much use. Too small for big jobs, like chopping wood, and too large for small jobs, such as field dressing game and food prep. If I could only carry one edged tool in forest and mountain wilderness areas it would be a large, high quality knife with around a 10" blade and finger choil.
A small axe, or hatchet, has its place, and I carry one in my truck, but for packing in I'll always take a large knife over an axe. A large knife is much more versatile, and has less weight and bulk. Since knives are such essential tools in the wilderness, I like to have a large knife as a backup for a small one.
Of course, it all depends what kind of environment you are in, what you need and want to do, how much weight you want to, or can, carry, etc. There is no "one size fits all" since everyone's needs aren't the same.