My wife makes them every single week. And never had anything but homemade meatballs growing up, nor did she.
It's probably not what you are looking for at all, but the best meatballs are made with pork. My wife makes them 100% pork, with some seasoning and some onions which helps retain moisture. I know Pork/Beef blends and Pork/Beef/Veal blends can be good.
I'm sure you are looking for a beef recipe so will allow others to take the lead. But in my opinion,when you are looking for recipes I would think the same way as making a hamburger, less is more. 80% chuck, don't compress them too much, and don't add too much stuff. Unless you're going for a meatloaf type consistency, I would skip too much breadcrumbs and eggs and that kind of stuff, and don't add salt. Some onion and garlic, some italian seasonings, and that's about it. Be careful stirring...one or two will probably break if you made it right.
If you end up with firm hard meatballs, that's not really to my taste.