Well...if you believe the historical research, a majority of ancient sword makers thought 16 degrees per side was it. Kind of like Mr. Ezell.
Personally, I think angle is job specific for the type of steel the blade is made from. If I'm gonna be using a mallet or stick to bang my old hunting knife through the pelvis and brisket bone on a deer and then expect it to cape out the deer cleanly afterward...which I DO, I stand the angle up to more like 18-20 degrees per side. If I'm sharpening a boning knife for the kitchen or small game knife it's more like 15 or so.
But all of that is contingent on the type of steel. If the blade is stainless, I always go with steeper angles because it is so much harder to sharpen when it gets dull. So I want it to stay sharp longer to avoid having to sharpen as often.
I know you stainless guys will say I'm full of it. But in my experience, easy to sharpen stainless is because it's left softer. Which means it will dull quicker and the steeper angle holds an edge longer in that case too.
But each steel has a character that plays into angle. 5160, properly heat treated will retain an edge better than 1095 that's properly treated. But it's also a little harder to sharpen. It's all about trade offs between edge retention and cutting ease. Just kind of a personal preference thing to my way of thinking.