Monitor
Throughout the DOS era, CRT (Cathod Ray Tube) screens were the norm - LCD (Liquid Crystal Display) screens were not introduced to the wider market until the later half of the 1990's.
Again, the choice is down to compromises, as both screen types has advantages and disadvantages. If you are a purist, a CRT is the way to go, but...
CRTs are big, bulky and heavy. The are often flickery, as they usually run at 60 Hz refresh rate. Stable, non-flickering images can usually be achieved at around 75 Hz, but the higher refresh rate often came at the cost of resolution - higher resolution, lower refresh rate.
They can be hard to find in good, working order today, as they usually loose some of their crispyness and brightness with age.
On the plus side, they do display clear, warm images. While CRT's do have a maximum resolution, its pixel-size are not fixed as with LCDs. This means that it can display resolutions lower than the maximum without interpolation, as it more or less changes the pixel-size to match the lower resolution.
LCDs, as you probably know, are far easier to place on the desk. Due to the way they display the image, flickering is not a problem, and you can easily look at a LCD with 60 Hz refresh rate all day long, without tiring your eyes (provided you don't set the brightness to high).
The problem with LCDs is interpolation. It is not as pronounced today, as it is less visible, the higher the (native) resolution the screen has. But for a DOS machine, you want a 4:3-format screen (a 5:4 is also acceptable), which limits your choice of resolution.
While you may be lucky to find a 1600*1200 LCD in decent condition, it is more likely that, if you choose an LCD, will end up with somthing along the lines of 1024*768, 1280*960 or 1280*1024 (the latter being 5:4 aspect ratio).
Lets take the 1024*768 as an exemple. This is the monitors "native resolution," meaning that the screen has 786.432 pixels - 1024 columns and 768 rows. If the screen gets a signal in the resolution of 1024*768, no problem - it will just display that. If it gets a signal of 640*480, all hell breaks loose!
Now, to make the image fill the entire screen, the screen wil resize it to 1024*768. This becomes a problem, as, this means each pixel of the original image now has to be 1,6 "native resolution-pixels" wide and high! But, as the LCDs pixels are fixed, two original pixels wil be stretched to three pixels on the screen (actually 3,2), interpolating the middle one between the two.
Imagine the first pixel is black and the second is white. When interpolated to three pixels, the middle pixel will become a 60% grey. And the fourth pixel will still contain 20% of the original pixel twos color, regardles of the fifth... And this is not just horizontal - the same thing happens vertically!
As you might imagine, it can pretty quickly look horrible. Some older monitors (and IBM laptops) have a function to not interpolate the image, but to just display the original resolution with a black border.
This doeasn't mean that it is always a problem. Diaplaying a 640*480 image on a 1280*960 panel is no problem at all, since 1280/640 is 2 - and so is 960/480. In this case, each pixel will just double and be shown as 4 pixels (2*2) on the screen.
