If you want to work with a SQL Database, then the Grid will be better suited for your scenario, since it has full integration with all ASP.NET datasource components (for instance SqlDataSource etc.), with batch editing, inline editing and many more features coming out of the box.
The Spreadsheet on the other hand is designed to work through providers, with the SpreadsheetDocumentProvider being currently provided out of the box. This provider is designed to work directly with an excel file. The Spreadsheet is currently in its beta release, with the official being scheduled for mid January 2016, where additions like Improved Toolbar, Context Menu, Filter Menu and others.
The choice is up to the developer. For a reference of the available features of both controls you can go to our online demos and documentation:
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