Both the 3 Series and the A4 have a lot of space in the front seats whatever size you are, though the BMW has a higher console between the seats which can make it feel less spacious than it actually is. In the back, there’s not much difference between them. Two tall people fit comfortably and a third can squeeze into the middle back seat for shorter journeys. If you have two children, either car will have all the space you need.
Each car has exactly the same amount of boot space – 480 litres, which is enough for a few big suitcases when you go on holiday. The BMW’s boot has a bigger opening and a squarer shape, so it’s easier to load. Both cars’ back seats fold down for carrying longer loads
If you need to carry even more, the 3 Series and the A4 are available as estate models: the 3 Series Touring and Audi A4 Avant. The Touring has a marginally bigger boot than the Avant with the back seats in place (500 litres vs 495 litres), but space is identical with them folded down (1,510 litres). The Touring’s back window lifts up without opening the entire boot lid, so you can load small items more easily.
If you prefer a slightly higher seating position, the Audi A4 Allroad is worth considering. It’s an A4 Avant with additional SUV-style design details and a higher ride height.