I did a lot of research into coilovers when I got mine. Looked at posts by others etc. Pleased with my FK Automotives and think I was one of the first to get them. Just cuz no-one has had a certain brand doesnt mean they are no good.
Look for:
TUV approved, which basically means they are tested on the car. Coilover make look good but doesnt mean it will work good, damping and spring rates are important.
Warranty, longer the better. Was told by the place I got mine that FK come with lifetime guarantee if fitted by a FK approved dealer.
Reputation, crap stuff gets sl*gged off quickly. Also some dealers will tell you if they have had problems with a specific brand if you know them well enough. Trouble is some places may poo poo a particular brand cuz they cant or dont stock it.
I based my decision on price (which included free fitting) warranty and the blurb. If you check a companys site and it is a bit amateurish or does not say a lot, why ???
Think H&R tend to be the top of the pile for coilovers, people will also say Leda, then (in no particular order) your FKs Avos and Gazs etc. Koni if you can get them too.