I do not buy pre-ground meat; I have a Braun Professional processor from 1995 that creates the best texture for my various needs. As already stated let the meat and fat be chilled firm but not frozen solid and in cubes small enough for thorough circulation inside, not too much at one time. My butcher gives me free gold in the form of prime rib fat trimmed from all his rib-eye steak cuts which I incorporate with whatever meat I want... Beef rounds, sirloins, chucks or even pork loin meat, lamb, chicken breast.
If you want the best new machine available today get a Braun MultiQuick 7.