If using ground meat, brown it in a skillet over medium-high heat with the diced onion and garlic until meat is cooked through and onion is softened, then drain excess fat.
Transfer meat mixture (or just start with onion and garlic if making vegetarian) to slow cooker.
Add both types of beans, crushed tomatoes, diced tomatoes, and broth to the slow cooker.
Stir in chili powder, cumin, paprika, cayenne pepper if using, salt, and black pepper until well combined.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, stirring occasionally if possible.
Taste and adjust seasonings as needed before serving.
Serve hot with desired toppings such as shredded cheese, sour cream, green onions, or crackers.