When exporting data for general use, we in the industry are likely to reach for CSV files; they’re basically plain-text, but with a sort-of agreed-upon structure — well, there is RFC 4180 but Wikipedia agrees that implementations are inconsistent at best.
For most people, though, Excel sheets are what’s used and understood. XLSX (aka OOXML) files have been the default file format in Microsoft Office for some years, replacing the proprietary XLS format of yore, and few will look beyond that. Excel sheets can contain considerably more complex information than CSVs, but due to their ubiquity and, perhaps, some level of ignorance, they’re commonly used to transfer simple collections of rows. Long story short: we’re tasked with offering Excel import options in our apps.
