Bring first 3 ingredients and 1 cup water to a boil in a medium saucepan over high heat; gradually whisk in grits. Cover, reduce heat to medium-low, and simmer, stirring occasionally, 15 minutes or until thickened. Whisk in Cheddar cheese and next 4 ingredients, whisking constantly until cheese melts. Keep warm.
Rinse collard greens. Trim and discard thick stems from bottom of collard green leaves (about 2 inches). Stack collard greens on a cutting board. Tightly roll up leaves, and thinly slice into 1/8-inch strips. Quarter chorizo lengthwise, and cut into small pieces.
Sauté chorizo in hot oil in a large skillet over medium-high heat 2 minutes. Add collard greens, vinegar, and sugar. Cook, stirring constantly, 2 minutes or until greens are bright green and just tender. Season with salt and pepper to taste.
Place about 1 Tbsp. grits onto each warm spoon, and top with collard mixture. Serve immediately.
We tested with Quijote Chorizos Caseros Home-Style Dry Sausage.