I tried a mirrorless. Have you?

I know both worlds, having used optical viewfinders of analog SLRs and digital SLRs, among them the *ist DS, K10D, K20D, K5, K5II and K1, for more than 4 decades now (the digital ones not that long obviously ...). I also have used the EVFs of compact cameras and MILCs from different brands and the displays of cameras without viewfinder like the Pentax Q series. the Pentax K-01 or the Ricoh GR.

For me it boils down to usability. Doing photography the digital way I sooner or later get confronted by a digitized version of the picture I see with my eye anyway; for me it's not really that important if meet the digital version early on - in the viewfinder - or a bit later reviewing taken pictures on the camera's display or on a another viewing device (monitor, tablet, smartphone etc.). For all I want to do with the picture later on - and I do like very much to share, to print, to do photo books - I always have to deal with the digital result that was created after I pressed the shutter.

So here my usability criteria for any VF type:

My ideal VF is uncomplicated, bright, lag free, gives me a full view of what will be on the picture (exact framing), allows precise and easy manual focusing in all light conditions (because I have many MF lenses), gives me enough information to allow me to control and adjust the camera without taking the VF from the eye and is not interfering with my ability to evaluate and compose a picture.

Is there a VF out there that meets all those criteria?

Not really. Here my personal findings for (D)SLRs / MILCs:

OVFs in manually focusing analog SLRs tick a lot of boxes for me; they allow for very easy manual focusing with their focusing aids (e.g. microprisms). They were routinely big and bright and of course lag free, and a lot of analog SLRs I used displayed the most relevant camera parameters (shutter speed, aperture, over- or underexposure) in their VFs. Their downsides were that manual focusing became less easy with not so bright lenses (the focusing aids then didn't work anymore) and that the DOF preview was pretty unusable with lower f stops (VF darkens too much). I never had an analog SLR with AF so I don't really know if focusing aids were compatible with it.

OVFs in AF capable DSLRs are also bright and lag free; but even the K-1's great OVF is no match in viewing size compared to what I have with my analog Ricoh XR7. Because of that and due to the missing focusing aids I had and have trouble with manual focusing in critical circumstances; for example I always switch to Live View on my K-1 for using the Samyang 85/1.4 wide open to be really sure where the focus is. Hand holding the cam at arms length for that is awkward IMO and does interfere with picture composition. YMMV of course.

The EVFs I use in MILCs are bright and and have no perceptible lag in normal lighting conditions; they do lag in very dark situations, but on the other hand provide good enough resolution even then for precise manual focusing. What I see in the VF can be precisely controlled (e.g. a free selection out of exposure data, live histogram, ISO values, levels, composing aids like grids and more), and often I can choose between different modes (e.g. exposure preview on/off, color filters / monochrome live view etc.). The EVFs I use of course have their limits when very tiny amounts of light only reaches the sensor (so e.g. DOF preview in very dark surroundings is pretty useless and AF-C can be limited in the same conditions), but on the other hand make things possible that simply are not with an OVF (e.g. getting a very grainy, but at least for framing purposes good enough view of a picture a pinhole optic will furnish). They have a plethora of aids for manual focusing, e.g. focus peaking and different steps of magnification. The use of the different modes available and of the focusing aids is not very intuitive though and has to be learned; if you have to fiddle around with the controls for choosing a mode more appropriate for the scene you are about to shoot that can and does get in the way of spontaneous picture taking, so more planning is needed compared to using an OVF. And don't forget your extra batteries!

As I said there is no clear winner, and no technique really ticks all the boxes for me. But I have to admit that down the line the usability of good and fairly recent EVFs (early low res ones with horrible lag I found unusable) is compelling, especially for MF purposes. I also value the ability to use completely silent shutter on some of my MILC cameras very much.

I have to state clearly that these are only my personal findings and preferences based on my particular needs, and nothing more.

Phil