Having used Leicas for a few decades with only the MP in 'foreign territory' (and if I find a chrome .85 may take the plunge!), my personal choice is the M4. I really do feel a difference between the classic Wetzlar cameras and the newer M4-2 and on. The M5 is my best 'M-series tool' to use, but favorite is the M4.
And as for rangefinder white-out... it does happen and my M6/M7 did suffer from this. But I worked around it and it didn't happen all that often, when it did, it took more time to focus. The best finder? I still like the M5, with the extra information - meter readout and area covered, 'basic' frames that I need in more true size than the M6 and later, and the runner up to the M3 for white-out protection - maybe its the combination of the glass (not plastic as in the newer cameras) condenser lens left out of the M4-2 thru M6 and earlier M7, and the different style light collecting window.
But I have to add, I think the best deal in 'classic' size M-series may be a good working M6 (qualify this as one having a good resent CLA for a 20+ year old camera). Having a built in meter does have advantages, and the M6 does everything that a camera like this is called on to do.
Any good working Leica can be creative tool that does its job, everyone has their favorites for reasons, maybe its why most Leica users have a couple or a few Leicas around the house.