I've got the Mach 1 struts/shocks in my 95, and my buddy has the Tokico HP's on his 99 GT. There is definately a difference in ride quality. The Mach's really help in handling, but don't slam the car around too much when you hit a bump. The HP's are just...stiffer. Plus, the Mach 1's can be bought used for pretty cheap.
Mach 1's: great for street, good for track use
HP's: good for street, better for track use