Preheat oven to 425°F. Prick the potatoes all over with a fork and carefully place directly on the oven rack. Bake until just tender, about 30 to 45 minutes (depending on the size of your potatoes).
In the meantime, in a food processor, combine the cubed cheddar, pepper jack, mayonnaise, scallions, dill pickle, pimientos, and a small pinch of salt and pepper. Pulse until combined and spreadable. Transfer to a small bowl and set aside.
Once the potatoes are cooked, carefully transfer to a cutting board to cool slightly, but keep the oven on. When cooled enough to handle, use a serrated knife to cut them each in half, lengthwise.
Carefully scoop out the flesh of the potatoes with a spoon, transferring the insides to a large bowl. You want to leave somewhat of a border inside each potato to make them stable.
Add the sour cream, pimento cheese, chives, granulated garlic, onion, a pinch of salt and pepper, and mash until combined and somewhat smooth. Fill each potato shell with the pimento mixture and then top with shredded cheeses and crushed crackers (if using). Return pan to oven and bake until golden brown and the melted, about 8 to 10 minutes. Remove from the oven and garnish with chives before serving. Enjoy!