I keep three fundamental groups of headphones, each of which fits a broad category of uses. There’s the open-back stuff when I want the best performance, the closed-back units for when I need isolation (usually just listening in bed), and IEMs (and similar) for mobile/portable use.
I only use headphones/IEMs for listening to music (and the occasional audio book when walking).
For gaming and movies I only use speakers…
And my selection of headphones in each category is down to finding a) a primary headphone of that type that performs the best, overall, for the widest possible band of genres and then b) adding alternatives for different flavors and to exploit their specific strengths with particular styles of music.
So, for example, among my open-back headphones the best “single” or “overall” headphone I know of is the Focal Utopia. To that I’ve added an LCD-4, which is primarily used for female jazz recordings, and other very intimate productions. I have the Abyss AB-1266 Phi for larger scale productions, music with heavy fast bass/sub-bass elements, and when I want some added “excitement”. And HD800S for raw resolution, stage, and transient performance with very fast, progressive or complex music (e.g. full orchestral works/classical pieces).
The HD650/HD6XX and HD660S are kept mostly for comparison purposes/review references and for use in determining system synergy amid components at different price points.