I struggled with this question too. After many test drives of both cars, I decided to order an X1 sDrive28i.
I agree with many points here, like X1 is cheaper and better value, 3-series is more a sport sedan.
What got me to decide was the size of the car. The 3 got a little too long for my taste. OK and the slightly cheaper cost helps. My fiancee also pointed out to me that the X1 is more unique looking than the sedan, which I agree with, and also took that into my decision.
I say test drive them back to back and ask yourself which car you enjoy more!