The BMW 3 Series along with the Mercedes Benz C-Class are both rivals that are very tough. While the Mercedes got made over the BMW didn’t.
The Mercedes Benz C-Class comes with the 2 litre engine and this offers 4 cylinders which gives out 241 horse power. you should be able to get around 24mpg if you drive in the city and when out in the country you may get about 31mpg.
There is the 2 litre engine in the BMW 3 Series and from this you might be able to get 23mpg when driving in the city and 35mpg when you take it onto the highway. It offers up 240 horses.
But would you go for the Mercedes Benz C-Class or would you choose the BMW 3 Series?