I have a 3" blade folding type knife I have had since high school. I am 61 now! It has field dressed and butchered many an animal, from deer, hogs, to lots of elk. I can break down an elk with this knife using the "gutless method" to ready to pack out in a little over 30 minutes, using nothing but the knife, no saws. It is all you need.
Lots of guys switching to havalon type "scalpel" knives and they have some great advantages, but I guess I am just too hard on them. I like a knife you can lean on and not break! Just my personal preference.
The secret to a knife like mine is to get one with very good/hard steel that holds its edge well. But that also means it can be hard to sharpen. For me the Work Sharp solved that problem.