my opinion.... coilovers are great.... if only setup correctly, they cant be setup to perfect height, camber, adjustment by hand, by a diyer
i would stay away from coilies for non track useage, harsh on the roads, especially in uk.
i would opt for a good quality, fixed height damping adjustable shock and spring setup.
koni fsd and eibach springs would be my choice.
the h&r cup kit is a quality piece of kit and would be my choice out of the 3.
afaik, kw and weitec are the same company, so they will be similar
i would spend the cash on the h&r then use some more to uprate other parts to improve the handling.
id only lower to 30mm max anyway, to avoid driveshaft rubbing and ruinig the ride too much, not much point having coilies to drop to 70-80mm if your not going to do it.
after lowering, a good 4 wheel alignment, uprated bushes, new top mounts and the ride and handling will be transformed.
my two penneth worth