Well, you should probably give some details about what you need to do with your computer
For instance:
* do you need mobility because you use your computer at both home and school ?
* do you need small size or can you deal with 17", 3+ kg machines ?
* do you need 10h of battery life, or can you deal with high-powered computers which often have less than 2h of battery life ?
* do you want to run lots of modern games at high framerates and detail settings, or compute things on the GPU, in which case you'll want a powerful GPU and usually a powerful processor ?
* do you want to run CPU-heavy workloads such as some scientific computations, frequent builds of large code bases ?
* do you want to run virtual machines, and "many" of them ? Then you could want > 16 GB of RAM; easy on desktops and higher-end laptops, but many low-end laptops can't do that.
* EDIT: do you need a large amount of persistent storage ? Clearly, >= 2 TB is esaier and cheaper to get on a desktop.
Clearly, for any given amount of money, you'll get a desktop computer more powerful than a laptop. But moving it around is annoying, as we know
Making a (desktop, mostly - DIY laptops are few and not very powerful, AFAIK) computer oneself is a way to get more control over it, clearly. For instance, in pre-made laptops, a powerful CPU and > 16 GB of RAM nearly always implies a powerful GPU, which is a problem for me - I care about the two first items, but not the third one, and frankly, GTX 2060 or higher takes a heavy toll on the money (and power) bill.
Some manufacturers provide fully configurable desktop computers, which can avoid the need to build a computer entirely from parts.
