Hey Chris and thanks for getting in touch!
To be honest, there isn’t one recommended theme that comes to mind. We do our best to make the plugin integrate with as many themes as possible — however, it’s tough if a specific theme has very set styles for form fields because those can override the plugin’s styles and jumble the layout around.
That said, I’ve seen successful implementations used with Divi, Avada and a few others from Rescue Themes. We use the default WordPress Twenty Sixteen theme as a baseline for compatibility, so anything that builds off that or maintains a similar level of styling options would work best.
Does this help answer your question? Please let me know. 🙂
Cheers!
Geoff