PornHub seems to be the porn benchmark of the internet. Here you have a fascinating visualisation that shows you the most viewed videos in relation to their category. On the left you can see all the videos ordered by views (3.2 billion in total!) On the right you can see the 15 categories they belong to. NSFW warning.
Click on expand to read the tantalising titles (pinch to zoom in in your browser once the image is expanded to see them clearly.) Obviously, most titles are NSFW. For a MEGA full-size image, click here.