To choose a tower pc or all-in-one depends on many factors. The advantages of 21 inch touch screen all in one PCs over tower PCs are that they take up less space, are more portable, can be touchscreens, and are very easy to set up. But relatively speaking, the cost performance, performance, and cooling capacity are slightly inferior to tower pc.
The advantage of a tower PC is that you can customize and upgrade individual components, including the display. CPU, memory, graphics card, power supply, motherboard, computer case, keyboard and mouse, etc. All can be individually configured according to your own needs. Cost-effective is the first choice for home and game players.