Two Sedans with some similarities, but otherwise different in most aspects such as the starting price, horsepower, fuel economy, and ground shadow size. First of all, the 2016 Cadillac ATS is priced $7,885 lower compared to the base MSRP of the 2015 Audi S3. Also, although the 2015 S3 has a more powerful engine than the 2016 ATS, it gets 1.8 more mpg. And finally, the S3 has a slightly smaller body than the ATS. Among similarities are the body structure, market segment, height, and maximum occupancy.