No conozco los Bilstein.
Aquí
http://www.autoanything.com/suspension-systems/koni-vs-eibach-which-suspension-parts-are-the-best.aspx tienes una explicación de la diferencia entre Koni y Eibach.
Y aquí
http://www.e90post.com/forums/showthread.php?t=720906 uno que parecer saber de lo que habla:
As far as I know (I am on Bilstein Sport & H&R Sport):
Bilstein Sport - monotube, high pressure gas (a bit more expensive to manufacture, better heat management). They are not adjustable. Generally regarded as a harsher alternative, but can withstand more punishment and offer higher damping abilities. Bilstein also have the HD damper, that is supposed to be a direct replacement for the stock xi suspension, but I am not sure it can be used with lowering springs.
Koni Sport (Yellow) - twin tube, low pressure gas.
As far as I know, they are considered easier to live with on a daily driving car. Single adjustable. Rears can come w/ external adjusters, so no need to remove the shock to adjust. Both TCK and HPA have come up with coilover conversion kits for them (offering height adjustability and high quality linear coilover springs - spring rates of your choice - a good step up in terms of performance).
If used in their factory form, both can be paired with either Eibach ProKit (linear) or H&R Sport (progressive) springs as their manufacturers claim they can work with lowering springs. During my research it came to my attention that the Eibach ProKit available in North America (#2092.140) is not specifically designed for AWD (our cars require slightly higher axle load ratings), while H&R has an AWD specific model. Generally, that did not prevent people from using the Eibachs and being happy with them. Consensus seems to be that Eibach lowers less and offers a more comfortable ride, while H&R is a bit more aggressive with the lowering and comfort.
I chose Bilstein and H&R because of the technology employed (Bilstein) and because I was set on using AWD specific products (H&R). I looked at the coilover converted Konis, but for my particular situation it was a bit overkill. Needless to say, I am happy with my choices. If interested, my notes on that particular setup are here.
Technical
Q: KONI makes some shocks that are not gas shocks. Why?
A: There are basically
three types of shock absorber designs: mono-tube high pressure gas, twin-tube low pressure gas and twin tube hydraulic (non-gas). Each of these designs has a certain ride and performance characteristics that can enhance the performance of a vehicle and KONI is the only company that makes three designs. KONI ride development engineers evaluate each new vehicle and can decide which shock design would best apply to that vehicle. Some cars respond to mono-tubes, some like gas pressurized and others don't. Most shock companies utilize only one or two of these style because it is less expensive for manufacturing but are therefore limited in design capability and function.
http://www.koni.com/car-racing/technology/faq/