It really depends on the category that fits the free site content best. If the content could fit multiple categories (like your interracial MILF gangbang), I recommend selecting the category that best fits the sponsor. If the content AND the sponsor (like gangbangsquad) could fit multiple categories, then it's up to you
Feel free to experiment with different categories to see where you can get the best sales. As long as the content actually fits the category you're submitting to, category selection won't cause you any problems getting listed.