ultimately one coil spring is essentially the same as every other,
besides the obvious design differences like overall diameter, height, thickness of coil, and progressive (typically the rears) vs. linear (fronts)..
so I would try to get the Best part and not worry about saving 10-20$ on each coil. check out the warranty, and reviews, ..
you prolly won't be able to get any "specs" on the springs but maybe you can get 'spring rate' or overall weight (heavier is better) and that would help you decide too