Well I personally would stick with only H&R or Eibach for springs as both mfg. have had a long reputation and they both make competitive race springs, and both offer more then one spring usually for a given application.

And you can find them easily at places like Summit Racing or the Tirerack.

If your car is 50,000mi or more I definately wouldn't do the springs without a set of OE replacement shocks at minimum, else a nice set of performance shocks like Tokicos, Bilstiens, Koni's, etc. would be wise too.

Eibach even offers a spring-shock package for some applications.

I have Eibach prokits, they are very daily livable, but not a huge slam like many like. But I drive my car when I take it out, I don't mow down speed bumps for show.

And just to add I've had my prokits on the car for 5 1/2 years now and they are the same today as when they were new. I had many many un-informed individuals tell me when I installed them, that they would sag and droop over time....I guess I'll keep waiting? (unlikely) And as a point your springs shouldn't ever settle or lower over time-period.