My Miranda D works perfectly...
For this list though I nominate Edixa. All of them. I've had five or six pass through my hands. Every single one of them had a dragging shutter. Very easy to take apart though, so not a big problem to fix this. However, all but one of these Edixas also had degraded prisms and mirrors. Which is a shame because the one good one I have is really bright, and the image is larger than on most M42 cameras. The last problem is that most Edixas won't actually work with regular M42 lenses. The aperture plunger does not travel far enough to push the pin on most M42 lenses. This is why companies made Edixa specific M42 lenses.
That being said the camera I have run the most film through this year was an Edixa Prismaflex. I just can't recommend one of these to anybody who is not mechanically inclined. Because they're all broken.