Two SUVs with some similarities, but otherwise different in most aspects such as the modifications, horsepower, fuel economy, ground shadow size, and height. First of all, a bigger engine usually means less mpg. But the 2016 Mercedes-Benz GLA-Class AMG GLA 45 4MATIC has a more powerful engine and it gets 3 more mpg than the 2016 BMW X4. Also, the 2016 X4 is both slightly larger and taller than the 2016 GLA-Class AMG GLA 45 4MATIC. Among similarities are the body structure, market segment, starting price, and maximum occupancy.