Audi A4 2.0T Pros:
Soft, luxurious, comfortable ride
Rear space
Boot space
Quality interior
Powerful engines with plenty of go
Highway fuel economy <7L/100km @ 125km/h
Cons:
Handling and drive not so sporty or accurate. Slightly vague steering, more of a luxury cruiser.
City fuel economy bad (10-12L/100km)
Multitronic gearbox isn't to everyone's taste and can feel like the clutch is slipping.
E90 BMW Pros:
It's a BMW
Sporty, accurate drive
Reliable
Cons:
Slow 2.0 petrol engine
Thirsty (10L/100km)
Rough ride, harsh tyres (runflats)
Cheap feeling interior
Cramped rear seating
Older look and style
That's my take, based on owning the A4 and having spent plenty of time in a E90 320i