Both Divi and X Theme are WordPress themes that are deeply integrated with a page builder. Of course, Divi is using the Divi Builder, and X Theme is using Cornerstone. Personally, I prefer the page building experience of Divi because it is both intuitive and more enjoyable. Divi also has massively more online resources and tutorials. From a cost perspective, Divi wins out since its $89 for unlimited websites, where X Themes is $59 per website. So if you are developing websites for clients, X Theme is going to be significantly more expensive as soon as you build your 2nd website. Divi completely dominates X Theme and Cornerstone in every regard.