Both Chris Lema and Pippin Williamson have written fairly detailed reviews of page builders. While I do not plan to replicate their work, I want to comment on an issue I ran into with the Visual Composer plugin.
Visual Composer is quite developer friendly, so that developers may add custom features and layouts that enhance a particular project. However, the customizations along with the plugin itself, are often bundled as part of a theme. As long as the theme developer keeps the theme and plugin up-to-date, this does not pose a serious problem. If the theme is no longer actively supported, both the plugin and the customizations can start causing trouble.
While a developer can fix the issues and get everything working again, this does not make for a very good user experience.