IMO, it depsends on how you define "important". Important as in "makes the most improvement for money spent" or "easiest to install". All the responders seem to think you are using the first option. If the second, then Strut Tower Brace is your answer.
My car has both plus a K member brace, a rear panhard bar, heavy duty u & l rear control arms, quick ratio power steering rack with steel u-joint steering shaft, aluminum drive shaft, Baer four wheel discs with 13" fronts and 12" rears, 17X8 TSW wheels with Yokohama "Z" rated 245/40 tires, Torsen rear axle with 3.55 R&P and SVO rear cover, Monroe yellow top shocks and struts. It used to be lowered 1.5" on both ends, but suffered fairly severe front tire drag on hard cornering, so I went back to stock height springs.
