Chuck works good or any other fatty, well marbled cut like short rib . You want enough fat so that when you cook it for a long time the fat will render and leave a very tender piece of meat. If you use something like sirloin, with little fat, it will dry out after a while and basically be like chewing on a tire. Texas chili uses actual chunks of meat instead of ground meat, correct? If so, then buying a chuck roast or boneless short ribs and cutting them into pieces would probably be best.