If i have to pick just one headphone, i probably go with sony ma900.
If I had to pick just one and had to choose between the HD540 or HD800, it would have to be the HD540. As much as I like the HD800, there is simply too much poorly mixed material that the HD800 is not enough forgiving of.
When the material is good, the HD800 can be stunning. But the HD540 is a better all-rounder. As much as I would like it that all my favorite artists got the sound engineering right, I have to be realistic and accept that many great albums are not optimally or even well mixed.