S4 Hand down, If it was a 330xi then it may have a chance but the S4 wins because of the fact that it is a tuned A4 which would be the 3 series competition, it has a 250 Bhp 2.7L Biturbo V-6 (Love that engine
) and it has Quattro which turns all of the wheels which puts th S4 way out of the 330ci's reach. The S4 does have one setback though, I found it to be smaller than a 3 series (I'm 6 2' so That is a problem for me) i'm not aying it's more expensive because BMw's options can really add up and the 330xi is competitvely priced with the S4.