Purpose should be the first reason, what are you gonna use it for? heavy gaming? light office/school work? facebook and websurfing?
once you know why you're buying the laptop for then that's how you can decide if you need an expensive more powerful one(for heavy gaming/or video editing) or a cheaper slower one(basic uses like web surfing/facebooking/youtubing/officework/homework) but does the job you intend for it to do.
For example, i simply hate those snobby little brats buying $2,000 macbook laptops and all they do is facebook. where you can buy a $150 laptop that can do everything what their doing on their macbooks.
