I have several high quality headphones. But my main use is for portable purposes. Most of them I never use, or are not suited for portable use in the first place; I just ended up starting to collect them at one point.
My main portable unit is the Sony MDR-CD900ST. I have never come across another phone as well suited to high fidelity, long term listening on the go, as compared to these, and I have tried almost all of the highly regarded headphones under extensive evaluation. The CD900ST is the most realistic tonally for acoustic, classical and jazz. If you prefer death metal or rap, you may not like them so much, as they have a somewhat subdued treble range. Build quality is 1st rate, and better than most, regardless of price. Build quality is very similar to the MDR-7506 in appearance, though it is a completely different headphone.
-Chris