With lowering springs you get just a new set of springs. They will lower the car, improve the handling, and will be stiffer than stock springs.
With coilover (full coilovers) you get the new springs, and a new shock with adjustable height. The benefit of these is the shocks that are built in are specifically matched to the springs used. You can also adjust the height of the car at any time.
If you have the money at your disposal I would very much recommend you go for the full coilover setup. Here are some brands for both that everyone here seems to like.
Springs Only:
Eibach Prokit
Eibach Sportline
Neuspeed
Full Coilovers:
Tein
Tanabe
I have Ground Control coilover sleeves with Eibach springs on my 'Lude and I love them. I gave myself a 1.5" drop.
Good Luck...