the eibach sportslines give a 1.8" drop to your front and a 2.4" drop to your rear.
this levels your cars stance out (takes the 'foward lean' away).
this reduces traction (which is bad) but it also reduces understeer (which is good) because a bit more weight is shifted onto the rear tires and this levels your weight distribution out a little more (50/50 weight distribution is what every car strives for--althoug the eibach sportlines will not affect the celica that much as to get 50/50 wd but it helps).
so, choose you're poison.
if you like to stoplight race or go to drag strips, then the pro-kit is better because handling isn't really needed in a straight line.
if you're style is geared more towards street racing, than the eibach sportlines are your choice.
if you're not interested in racing and you're more interested in style (no one can blame you) then the sportlines are also your choice due to the increased lowering and evening out of your celicas stance.