This is all going to be a preference thread. Everyone is going to say what they like and give little to no reasons why. My opinion to wanting coilovers is this:
Coilovers are good. Cheap coilovers are not. Any coilover set up that is under 1300 is not worth getting. You would be better off getting Koni Yellows with ground controls. It will be a lot better set up and it comes with a lifetime warranty, which is WAY better than the 1 year the tein come with. Koni is one of the best shock manufacturers offered for our cars and it is weird to me that people do not take advantage of it more. Another perk to look at having a 2 part system is that Koni focuses on the valving. That is all they are worried about, ground control focuses on the sleeve and eibach focuses on the springs. This means all 3 companies are specialists and only have 1 thing to worry about. When a company has the whole package it costs them a lot of money and in order to sell it at a budget price they skimp on quality. Making a coilover is not cheap, which is why good ones are expensive.
I am starting to ramble here...it has been a long ass day, but to sum it up; Cheap coilovers like tein basics, and function form have shitty valving and retarded spring rates. Yes they work, but are they worth getting over the koni yellows? Nope. People frown on the koni gc set up because it isn't a "real" coilover. Well it is set up better than most coilovers that are even double its price..I will take that over having a "real" coilover any day. I care about performance, not name.