Agreed, the proper head to head will be the S4 against a similarly equipped M Performance 335i.
Autobild gave the 335i the nod by 10 points overall due to a 14 point win in the cost category, the S4 won the driving dynamics, comfort and body (interior exterior) categories. In the UK the pricing for the standard 335i (335i Luxury Auto) is £38,355 vs £38,645 for the S4 S-tronic. Basically, for a UK buyer (where price difference is negligible) Autobild has given the nod to the S4. It will be interesting to see the price of a 335i with the M-Sport pack and the M Performance Power Kit (hopefully that includes bigger brakes and an LSD) compares to the S4.