There are literally hundreds of porn niches, some are more profitable than other ones for various reasons. Cams and datings are the two most profitable niches, but you can still make good money with other ones.
Before choosing a niche, it is recommended that you check out your competitors, how much traffic they get, how do they make money (do they sell ads, promote premium paysites or do sponsor posts), how much followers they have on the social media (Twitter is the most popular one for sites, since they are the most adult friendly).