Never had a problem with the H3 but it was my first SLR and I really babied it.
Have had 3 MX's, one dropped on concrete with the 85/2 had the mirror knocked out of alignment and a dent in the prism housing. Having the mirror realigned was not expensive. The other one I had back then never had any problems. The one I currently have looks to have been knocked around quite a lot, but works fine. The wind mechanism seems to wear out faster on MX's than it should, going by how many I have handled that were obviously sloppy there. The metal (top and bottom plates) is pretty thin, I wish they had used a gauge heavier metal and let the camera weight an ounce or two more.
The current ME Super toppled off the desk onto the cushioned chair and then onto the floor. Cracked the plastic top plate, but otherwise works fine. The one I had to sell awhile back never had a problem. However most of the ME, ME Supers I have seen have never had the heavy use most MX's have had.
Of the three models, the H3 felt the most solid, but I do not think it would have stood up to the use and abuse I gave the 2 MX's I had when when I was a working photographer, I would guess the same would apply to the K series cameras as they are basically the same under the skin. I never trust electonics for long term durability, I have had too many electronic gadgets go out for no apparent reason over the years, so no camera that is dependent on the electronics would fit "toughest" in my mind. So, I guess I would have to go with the MX (if you could get a new one).
-- graywolf http://graywolfphoto.com
"You might as well accept people as they are, you are not going to be able to change them anyway."
