Short version: test drive both
Lon version: I'm an E90 (328xi) owner, and I am awaiting delivery of my F30 (328i, since xDrive can't be had with 6sp).
The car did feel a bit softer (pro for my wife) but at the same time, once in Sport mode, it felt imore agile/nimble and it was holding the road _really_ well (this was a Sport line model, which is the line I chose). I know it has 1" more legroom in the back, but overall the car felt bigger inside (while being overall lighter!)
Eco/Confort mode are definitely "numb", but I consider that a plus when, say, driving around the in laws and what not; but even my wife has said she'll most likely be driving in Sport most of the time.