I can't say that I've ever used a recipe for meatballs...
As with so many other dishes, including meatloaf, I just... make them... with whatever sounds good to me at the time.
The only givens are some form of starch (usually bread crumbs), an egg, onion, garlic (LOTS of garlic), basil, oregano, and some milk or (normally) half and half.
Optional ingredients include grated carrots or beets that have been sweated, Worcestershire sauce, ketchup/tomato paste, fish sauce or various kinds of hard cheese.
I never measure the ingredients, I just throw in what looks right.