Prepare the salts in 3 small bowls: Mix the Maldon salt with the orange zest, the kosher salt with the paprika and the smoked salt with the black pepper.
Light a grill. Drizzle the corn with vegetable oil and rub to coat the corn thoroughly. Grill over moderate heat, turning often, until the corn is lightly charred all over and just tender, about 15 minutes. Transfer the corn to a large platter and serve with butter and the seasoned salts.