Stationary computers do not always come in the guise of metal boxes; they run the gamut from tiny to mighty. To help determine which design suits you best, I've created a short quiz for you:
Tried and tested, the computer tower is the pinnacle of comfort, cost-effectiveness and durability.
Not venturing too far from the original, the compact tower sacrifices only a little to save you a bit of space. Some of them can even be used horizontally and placed under the monitor as a monitor riser to save some space.
Shrink the stationary computer as far as it will go and you get a device smaller than a box of tissues. Great option to plug to a TV set or on a desk where there isn't space for a tower at all and high performance is not needed.
Monitor and computer all rolled into one. This is the best-looking option in exposed spaces where you want to keep the wiring to a minimum. The single-device approach is also a boon for the frequent mover.
Of course, those recommendations are based on what's typical of each of those designs; there are exceptions. Those exceptions could however be hard to find and expensive in comparison.