When you are trying to decide between 2 different lowering springs you have to figure out what is more import to YOU first.
Individuals are different and this is what I caution my local clients against. Don't follow the crowd to closely as it may not be what you are looking for exactly.
The first step is too understand the differences in the lowering springs out there and then make the call based on what appeals to you more as a potential buyer.
Here is a brief overview of the differences between the H&R sport and Eibach lower springs:
H&R - Uses a very stiff 54SiCr6 alloy spring steel that has a higher progressive spring rate than the Eibach springs. That results in less body roll and firmer more precise suspension control. It also reduces the travel of the struts and shocks more than the stock (OE) springs. You gain more control over the suspension movement at the expensive of ride quality.
Eibach - Uses a high strength, high toughness spring steel called "Hi-Ten" in their Pro-Kits. The progressive rate of these springs is not quite as stiff as the H&R sport springs. Eibach focuses more on engineering a balance between ride quality and precise suspension control. Eibach springs will provide the exceptional handling and precise vehicle responsiveness and stability with minimal effect to the ride quality. Eibach engineers are very good at achieving that perfect balance. (optimizing handling vs. ride quality) Eibach springs are designed to allow the suspension to move in a controlled and predictable manner, and they do not compress the OE struts and shocks too much. That can lead to ride harshness that you won't particularly like.
There is a breaking point in regards to aftermarket lowering springs. A spring kit that lowers the vehicle too much, will inadvertently restrict the suspension travel, which results in a less comfortable ride and uneven handling characteristics. The vehicle may skip over bumps and road transitions, causing the tires to loose contact (adhesion/traction) with the road surface. A race prepared vehicle has a chassis and suspension designed for use solely on racetracks. The requirements for an everyday, street-driven vehicle that encounters potholes, expansion joints, weathered tarmac etc. are completely different. Eibach spring kits lower the vehicle center of gravity properly while properly maintaining adequate suspension travel. They have resisted the urge over the years to offer a more "aggressive" drop to their lowering spring kits, and in discussions with their chief engineer a few years ago...I think I know why that is the case. Eibach believes (and I tend to agree) that lowering a vehicle too much is counter-productive, because you will likely end up riding on the bump stops. This is compounded by the fact that OE shocks do not respond very well to being compressed more than the factory springs would allow under normal circumstances. The ride quality will decrease as a result. Eibach Pro-Kits are designed to work with original equipment shocks and struts. The lowering springs MUST NOT impede the suspension travel beyond a certian point...if you want to maintain good performance, and ride quality. (at the same time)
Bottom Line: Every suspension set-up is a critical balance between two contradictions:
Making it as soft as possible...while maintaining some measure of control. (which requires some spring stiffness) Finding that balance between the smooth softer initial characteristic for increased traction and comfortable cruising, while also maintaining a stiffer final progressive rate (as the spring compresses under load) for reduced body roll and better responsiveness under curving, braking and accelerating. That's a very difficult combination to pull off. (he went with the eibach)