General Motors, the world's biggest car maker, has chosen its German unit Opel over Swedish subsidiary Saab to make its mid-size cars in the future, the daily Frankfurter Allgemeine Zeitung reported on Monday. The decision will guarantee, at least until 2010, the future of Opel's main German site in Rüsselsheim near Frankfurt, the newspaper said. Rüsselsheim was competing with Saab's Trollhaettan plant to build GM's new mid-size cars in Europe, including Opel's Vectra model and Saab's 9.3, aimed at competing with BMW's 3-series and Mercedes's C-Class. In addition, GM would base all research and development activities at the Rüsselsheim site for its compact car, the Opel Astra. But the future of Saab's Trollhaettan plant was also secure in the medium term, since it would build the Cadillac BLS model until 2007, the report added.