In a medium bowl, beat the cream cheese and blue cheese with an electric mixer until smooth and creamy. Add the cheddar cheese; beat until well-blended. Spread in a shallow serving bowl or plate. Cover; refrigerate at least 1 hour to blend flavors.
Meanwhile, caramelize the onions: Heat the oil in a large, nonstick skillet over medium-heat. Add the onion; cook and stir 2 to 4 minutes or until tender. Reduce the heat to medium-low; stir in 1 teaspoon sugar. Cook for 10 to 12 minutes or until onion is soft and golden, stirring occasionally. Remove the onion from the skillet; set aside.
In the same skillet, combine the cranberries, sugar and water. Cook over medium heat about 5 minutes or until the cranberries begin to pop and the mixture thickens, stirring occasionally. Stir in the vinegar and onions. Cool slightly.
To serve: Bring the cheese spread to room temperature. Spoon the cranberry mixture over the cheese spread and sprinkle with walnuts. Serve with assorted crackers.