Audi tends to have slightly lower maintenance costs over the long run, but BMW offers a more engaging driving experience. Consider the specific engine; some BMW engines (like the B48) are known for better reliability than others. For your budget, a well-maintained, lower-mileage Audi A4 2.0T might be the safer bet for reliability and comfort. Test drive both and get a pre-purchase inspection from a trusted mechanic familiar with European cars.