You usually get more for your money with a PC than with a laptop.
So if you spent �500 on a PC and a laptop the PC would probably have a faster processor, more memory, bigger hard disk and a larger screen.
Also hard disks in PC spin faster than those in laptops so are better.
But as others have said, there are other advantages in having a laptop, like portability.
Note that a laptop screen is unlikely to be more than about 15" (although there are some 17" laptop screens)
A PC screen is almost certainly going to be 17", with more and more offering 19".
If you are doing a lot of work with digital images, videos, or even writing computer programs, then a 19" screen is great, once you have one you would not want to go back to anything smaller.
It is all down to how you are going to use the computer, fixed in one place, or on the move.