PMPExR, the disadvantage of the TEIN NA/HA coilovers is that if you want to replace the coils at one point, you can't be able to swap it out. I did hear on my board that there are now a couple of places (in the US anyways) that can replace TEIN coils for you. Don't get me wrong...I wanted TEINs at first, but I wanted coilovers where I can replace components when I need to.
As for Ground Controls, it all depends on the spring rate your friend has. I have 450 lbs front/380 lbs rear...far stiffer than any aftermarket spring, over twice the spring rate of stock. So, riding in my car is pretty rough, but that's my personal preference. I got the spring rates for autocrossing/road/track purposes, not for style. The advantage of GCs are that you can replace any portion of the coilovers easily. If I so choose, I can swap in/out either stiffer (up to 650 lbs) or softer coils. I haven't had any problems adjusting my coilovers up or down (gotta jack up the car to get to it though), and customer service at Ground Control is great.