SingleFile is suitable for almost all content-based web pages, while WACZ will only be used for pages that SingleFIle cannot fully archive, especially dynamic web pages (web applications) that will change the rendering data within the page with interaction. But if you can only choose one to suit all situations, then WACZ is the only choice. I used to build my own private web archive workflow and finally chose SingleFile as the main target archive format. WACZ is an alternative in extreme cases. In general, I do not think that web archives should allow readers to interact with web pages. If so, I will save multiple versions for multiple dynamic versions.