If you're serving this dish at a party, you can keep it warm, covered, on low-heat setting for up to 2 hours. Just stir it occasionally.
Trim fat from meat. If necessary, cut meat to fit into a 4- to 5-quart slow cooker. Sprinkle meat with the 2 teaspoons smoked paprika, 3/4 to 1 teaspoon black pepper and the salt; rub in with your fingers. In a large skillet, brown meat on all sides in hot oil over medium heat. Drain off fat. Transfer meat to cooker. Add onions, undrained tomatoes, apple juice and garlic to slow cooker.
Cover and cook on low-heat setting for 10 to 11 hours or on high-heat setting for 5 to 5 1/2 hours.
Meanwhile, for barbecue sauce, in a small saucepan, combine ketchup, vinegar, Worcestershire sauce, the 2 to 3 teaspoons smoked paprika and the 1/2 teaspoon freshly ground black pepper. Bring to boiling; reduce heat. Simmer, uncovered, for 15 minutes, stirring occasionally. Remove from heat; set aside.
Transfer meat to cutting board, reserving cooking liquid in slow cooker. Shred meat with two forks.
Pour cooking liquid into a 4-cup measure; skim off fat. Return meat to slow cooker; stir in barbecue sauce and enough cooking liquid to reach desired consistency. Cover and cook on high-heat setting about 15 minutes or until heated through. Serve immediately on toasted buns. (Or keep warm, covered, on low-heat setting for up to 2 hours. Stir occasionally.)