I just bought a 2004 S4and have been in love since I drove it off the lot. I want to make the stance a little more aggressive, so I'm looking to buy some coilovers and then a set of 19" RS4 wheels. I'm leaning toward the Bilstein system, but I wanted to get some feedback before pushing the button. Thanks in advance.

 

There is endless coilover systems out there.... anythign will be very good, but some have a more agressive feel with them. im not too familiar with 04 S4's but i know different companies use different springs and such. Like for B5's the Vogtland have a nice tight system with less give, However something like the Koni coilovers are a little softer and you get a nice bounce from the springs.
goto PureMS.com and see if they have any customer reviews for any of the S4 suspension or try awe or asp

 

My vote is Vogtlands. It's not harsh at all, adjustable, high quality, not to expensive.

 

I'm very happy with my KW setup. I've also heard good things about the Vogtlands (that are probably less expensive). Mixed reports on the Bilestein (PSS9s)and I've found them harsh (as a passanger - but don't know the settings - probably full up track settings). One thing to say on KWs behalf is that they actually have different units for Avant versus Sedan. I really think that they have engineered their coilovers very well. I've left mine at the (recommended for street) medium setting and the car rides great (not too harsh at all) yet is very responsive, capable and stiff when needed.

 

my buddy has tein coilovers in his 01 s4 and his mechanic told him not to put the jap suspension in but he did it anyway and he LOVES IT..his mechanic then told him he did a nice job and choice....ill probly do the szame...TEIN..

 

I've got the eibach pro streets on my car, and they're great. Feels very close to stock in terms of comfort, yet more aggressive. Also, the price is good.