Choosing the right desktop PC can be difficult, especially with the form factor. But here are some good rules of thumb.
All-in-One (AIO) PCs are great for those who prefer a clean setup with as few wires and cables as possible. AIOs just look better because you don't see the computer part, just the display. You also get everything in the box making it a simple purchase. The downside is they can be difficult to upgrade down the road and can be tricky if something breaks. But they're awesome looking family computers and are super convenient.
A traditional desktop tower lets you bring your own display, keyboard, mouse, and speakers, which is good for those who want a high-end 4K display for graphics work, or a specific gaming mouse that they know is good. The cons of a tower is they can be a bit messy with all the cables and ports.
Finally, a gaming desktop PC is king. It offers the most flexibility, has the best cooling systems, and tends to lean into the latest hardware. It offers a ton of expandability and often has a flashier design with RGB lighting and aggressive aesthetics. The downside of a gaming desktop can be price (as they can go into the multi-thousands of dollars), and not everyone enjoys the look of some gaming desktops, which could look a bit juvenile for some.