All of these are based on pretty much the same technology so they put about equal strain on your eyes. I would suggest installing a small piece of software called f.lux - this will adjust the white balance in your monitor depending on the time of day and the lighting you have. This should make viewing the monitor more comfortable after dark.
all of them are different types CRT monitors hurt eyes more than other, where as other don't do much damage. having significant distance can keep the eyes safe.
2, 3 and 4 are technologies used in monitors. (A monitor is the thing you see the computer's display on.) If you mean CRT for #1, there's no difference in how good or bad any of them are on the eyes, if used properly. (That means don't sit 3 inches from a 27" CRT monitor or at a 150 degree angle to an old LCD monitor). (Eyestrain isn't damage to the eye, it's fatigue of muscles, and it has nothing to do with the type of display.)
basically there's not much of difference IMO, but LED screens uses least power and has least radiation to your eyes.