Purchase decision: Mazda 6 vs. Bmw 3er (F30)

I am faced with the purchase decision: Mazda 6 or BMW 3 Series (F30). 318dA or similar Limousine, Diesel, Automatic, Navi are especially important to me. Pro BMW: find the 8-stage automatic and Navi better in the BMW. Sportier. Pro Mazda: Better equipment for less money. Spacious. Quiet diesel. Price up to approx. 30,000 euros. Therefore, a young used person at BMW or Mazda comes into my question. Sure, am here in the Mazda Forum. But can you give me advantages and disadvantages to make my decision Thank you.