If you are using it for gaming and doing some graphics-intensive
work, I recommend you build one yourself. It costs less and you get
to choose the components that you like.
If you are using it for typing things out like writing letters,
preparing presentations, surfing websites, then buy a package. You
will be guaranteed of service when it breaks down.
For custom build computers, when components break down, you have to
go to the respective company and ask for exchange if the warranty
hasn't expired. Check your warranty card on where to exchange.