Preheat oven to 375°
Place potatoes in large saucepan. Cover with water and bring to a boil. Reduce heat to simmer. Cover and cook for 15-20 minutes or until tender. Drain. Cool until you can scoop out the middle, leaving a thin shell to stuff.
In large bowl mash the scooped potatoes with the butter. Reserve 1/4 c. of the Parmesan cheese, 1/4 c. of the cheddar cheese and 1/4 c. of the crumbled bacon for garnishing the tops of the potatoes later. Add the remaining cheeses, bacon, sour cream, eggs, onions, salt and pepper to the potato mixture. Spoon the mixture into the potato shells. Top with reserved cheese and bacon. Place on baking sheet and bake 20 minutes at 375°.