I got TEIN in my car and it is the best I've got so far. I tried things like Tanabe Sustec Pro, Eibach, Apex'i, Koni, AC Schnitzer in my Bimmer and I think nothing beats TEIN. In fact, I'm pretty sure it is the best suspension in Japan.
Never tried a GAB, and I gotta mind you that TEIN is, depending on the model, HARD! I suggest you check with them, what type of TEIN is that... They are much more expensive than a GAB, too!