Much prefer brighter/cool signatures as preference, I enjoy clarity, detail, air, separation, crystal clear mid range. I can handle a hint of warmth long as detail and technical abilities intact beneath, only when you venture into a dark mid range then instruments start smearing and vocals sound like someones singing behind a wooden door or wet piece of carpet, no thanks, I cannot accept that as good sound quality, I also find it very hard adjusting between the two opposites always leaning for the brighter piece of gear first.
Edited by H20Fidelity - 1/16/14 at 4:37am
The way I see it your preference probably lies where ever you can easily adapt, for example, if you find your struggling to adjust to a new signature (for my case warm/dark) I don't really find that enjoyable at all. A good purchase to me is one you put on after open box and say 'hell yeah' this is what I like (or within reason a day or so). Not one you're painfully trying to make your brain accept because several others thought it was great.
I've had some pretty shocking IEM's in my time here, I won't go into model names, although how some people can find those enjoyable is beyond me.