Preheat the oven to 180°C. Coat a gratin or other baking dish with cooking spray. Pick over the crabmeat, discarding any shells and cartilage.
In a medium bowl, mix the cream cheese, mayonnaise, Cheddar cheese, crabmeat, lemon juice, hot sauce and Worcestershire sauce. Transfer to a shallow 9x13 inch baking dish. Garnish with paprika.
Stir the ricotta cheese in a medium bowl until smooth. Mix in the onion, horseradish and Worcestershire and Tabasco sauces, then gently fold in the crabmeat. Spoon into the baking dish and smooth the top.
Bake in the preheated oven 30 minutes, or until golden brown and bubbly.
Combine the breadcrumbs and paprika, and sprinkle evenly over the crabmeat mixture. Bake for about 20 minutes or until bubbling. Serve piping hot with crackers.