Hello,
FE and FM supports the Pre-Ai lenses (so thats a pus point) so you don't have to do conversion if you own the older lenses.
FE2 and FM2 has a maximum speed of 1/4000 (1/1000 for FM and FE i think)
Otherwise pretty similar IIRC.
FM/FM2 are mechanical cameras (shutter moves by mechanical parts ie. springs, gears, etc) so in a way, it will function without a battery (meter will not). FE/FE2 are more electronic. Shutter is controlled by electronics coupled to the meter. Shutter will only work at 1 default speed if there's no battery.
Most think that full mechanical parts are more robust and reliable in the long run. However, being a mechanical engineer, mechanical parts do fail due to fatigure (too much usage), creep, plastic deformation, etc. So in a way, I do believe in that its more to do with luck (what condition your camera is in, was treated)
gd lucks =)