The Fuji GW (670,680,690) series is the toughest, there really is no comparison. The plastic body is sturdy, and absorbs shocks from drops and falls, the leaf shutter system is simple and reliable, and access to the important parts is possible with a minimum of tools. The only weak link is the winding lever, which can be broken off. The 645 is not as sturdy, don't let the little crash bar in front of the lens fool you, you can pull it off with your hand if you try.
The Fuji s are certainly good cameras and they stand up well. But I sold both of mine in favor of my Crown Graphic.
I think the Crown/Speed Graphic with Graphic 23 roll film holders is probably the toughest medium format rangefinder you will ever find. That wooden body absorbs amazing punishment and keeps coming back for more, even by wild and woolly Boy Scouts who have used (and abused) mine for the last few years trying to earn their photography badges.
The rangefinder has not lost accuracy in well over 10 years of use. The rangefinder contrast is still great and it is very easy to focus quickly. If the rangefinder ever did conk out, you could always fall back on the GG, which is a very useful Plan B.
Although lenses can quickly be changed, it does take a little time to re-collimate the rangefinder, though with the later models, focus cams can be built in advance if you know which lenses you want to use.
With two or three Graphic 23 film holders you can change film backs at will, going from color, to black and white to chrome in just seconds. If 6x9 isn't good enough 4x5 can quickly be substituted.
Finally, since weaponry seems to be a necessary criteria here, the Crown could be relied upon to protect you in a dark alley if needed. Light it ain't
I know they lost out to the Rolleiflex as the press corps camera of choice, but they are certainly a terrific rangefinder.
But it won't make a good anvil and I doubt it is bullet proof (with the possible exception of those bellows which are still original on mine.)
