17 reads at the time of writing and no one appears to have a view* either way. I'll answer my own question.
The best EVF I have ever looked through was on a Leica SL. It is the closest to the reality of an OVF which I have seen. Besides the obvious issue, the camera and native lenses are just too large and heavy. Even if I could afford the SL, I would be reluctant to carry it around.
The least satisfactory EVF I have used was on a Panasonic G3, largely because the colours were so muted. Until I got used to it, I found myself composing the scene, then taking my eye from the viewfinder to see how it really looked.
Normally, I prefer an EVF, mainly due to the abllity to see level and histogram information. Of the two, level is more useful. Like many people, I find I do not always instinctively hold the camera straight. Unfortunately, the E-M10 does not allow me to see both at the same time. I am not sure if Olympus has fixed this in its latest cameras, but it is a quirk given how configurable their cameras are otherwise.
Fuji does present both level and histogram simultaneously. The two cameras I use, X-Pro1 and X-E2, have older technology which limits their utility. The EVF in the X-Pro1 is not very bright, which makes it difficult to see in anything other than dull conditions. Fortunately, it also has an OVF on which level and histogram information can be overlaid. However, the OVF does not zoom and the frame lines simply get smaller or bigger as focl length changes. There is a magnification option, but the system is best suited to shorter focal lengths. The other issue with the X-Pro1's EVF is lag, which is significant. Trying to compose when something is moving in the scene is fraught with difficulty because what you are seeing is ancient history.
The X-E2 is better, being brighter, but the lag issue is not wholly resolved. Still, it is good enough for much of what I do. (Subtle humour there.

) Fuji does seem to have improved things with the X-T2, which has an EVF which approaches the one the one in the Leica SL. I have not done a side by side comparison, but I suspect the Leica is better as it has a higher resolution. The X-T2 eclipses F'uji's other current models, which would make it my choice if I were buying.
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