In my humble opinion it all depends on your needs. If you need a small, portable computer to carry it with you wherever you go, or you don't have much space on your desk, then buy a laptop. Laptop is a little bit more expensive than desktop and less efficient, but not everyone needs a very fast computer, e.g. businessmen.

Desktop is a good choice when you work at home or in office all the time. It offers you faster CPU, bigger hard disk and more efficient graphic card than laptop for less money.

Buy what you need