I personally love my S4 as my daily driver and my modded M3 as my weekend and track day car.
I have come across a stock B8S4 on the track and as much as it doesn't feel as sporty as the M3 it really does perform very good.
I'm actually thinking of bringing it to the track the next time I go to see how I personally do vs my M3.
As far as looks of the S4 over the A4 ... It stands out a hell of a lot more than the 335 over the other 3's ...
Only way I can tell a 335 over another 3 series is if I can see the exhaust although it does share the dual exhaust of the 335d.
The S4 has quite a few differences over the A4.
-silver lower front spoiler
-silver rear lower spoiler(whatever it's called)
-2 double exhaust tips like the M3
-front calipers that say S4
-V6t on both left and right fenders (I changed mine to the "supercharged" badge. No idea why they put V6T.
The S4 shouldn't even be compared the M3 since it's a direct competitor to the 335.
I guess people do because the V6 supercharged S4 performs about as good as the outgoing RS4 which used to be compared the current M3.
I have 27,000 kms on my S4 without any problems whatsoever.
2012 E92-M3 Space Grey on Fox Red, DCT
2011 B8 S4 S-Tronic , Black on magma red