Combine all dipping sauce ingredients, mayonnaise, ketchup, Worcestershire sauce, horseradish, 1/4 teaspoon smoked paprika hot sauce in a small bowl. Mix well.
Taste. Adjust seasoning to taste.
Set aside. (This can be done in advance. Store in a tightly sealed container, in the refrigerator, until ready to use.)
Separate onion slices into rings.
Pour buttermilk into a large bowl.
Add onion rings and soak for 30 minutes. (This tenderizes the onions and helps the coating stick better.)
In a large bowl, add flour, cornmeal, panko breadcrumbs, garlic powder, onion powder, 1/2 teaspoon smoked paprika, cayenne pepper, salt and black pepper.
Remove onion rings from the buttermilk, letting excess drip off and dredge each ring in the flour mixture, pressing gently to ensure a good coating.
Place coated rings on a baking sheet.
Pour about 2 inches of vegetable oil in a deep skillet or heavy-bottomed pot.
Place over medium high heat and heat to 350°F (175°C).
Add onion rings in batches for 2 - 3 minutes and fry on each side or until golden brown. Avoid overcrowding the pan.
Remove to a paper towel-covered plate to drain. Set aside and keep warm.