JKaptchinskie,
I have been running KORE suspension for several years, and the springs are great. I do not personally know the quality of the other aftermarket springs available so I will not comment there. I do know that KORE has spent a lot of time and effort to design the best coil springs possible. If you wait long enough though, someone will eventually come on to this thread and tell you their's are better.
If you go with aftermarket springs you will probably need slightly longer shocks, which means you are essentially buying a leveling kit. There are exceptions, but I have not seen a good quality stock replacement(height) spring yet. I have seen some attempts but nothing of high quality.
KP