Ideally, you want a good blend of say chuck and brisket, from a good butcher. I know not everyone has access to or money for that, but you can still make stuff that’s equally good from the supermarket meat counter. As long as it has at least 15% fat, you’ll be onto a winner, as the fat is what gives the meat a good dose of flavour. Never season the meat when mixing it up, and never add egg, breadcrumbs or anything else. You just want the meat. Adding salt to the meat and then mixing it up will cause the beef to start breaking down and you’ll get that very cheap sausage meat texture when you’re biting into it.