Like Ma Facon, for beef I use the Round and Chuck although for pork I use Boston Butt. Also this is generally at home only. Most of the Health Departments in the areas I worked eliminated the ability for Restaurant properties to gind some of their own meats. So....With the beef, sometimes I'll save scraps from cutting/trimming steaks and freeze then add to the round depending on the scrap. When I use Chuck I do trim off a good portion of the excess fat. A general rule for this is that the cap and large clumps of tissue seperating fat are generally bad while the smaller amounts of marbeling fat is okay. This was the same method I used professionaly and when I had access to a burger tester and it was common place to grind meats in house.... It usually worked out to be 80/20 on average. Although Round is flavorful in and of itself, understand the fat gives allot of the flavor to the ground meat. So round, being rather lean, will need to have some fat added back into the mix. This is why I save the trimmings.
Pork? I usually take the same approach as with the chuck only utilizing the Boston Butt. Lotsa flavor there but then again allot of fat too.
When grinding either I always use the coarse plate but pass the meat thru twice. This does a good job breaking down the fat into something that will cook out well but leaves the meat with more of a chopped steak kinda texture.