I can not give you a definitive answer, since it depends what you prefer to do but I can say that videos are more engaging and most people prefer watching videos than pictures. Now, if you are going to host these files on your own servers, then videos will eat up lots of bandwidth and disk space very quickly, so it is better to embed them from other porn sites.

If you are going with the WordPress, then you can upload some pictures and embed videos from PornHub or XVideos and use the KenPlayer plugin on your site, so it will look like the videos are hosted on your server since this software uses its own player to block all ads that tubes show on embedded videos.