Please let's not perpetuate this false stereotype. Pit bulls, if properly socialized, make wonderful family pets, just like any other dog. They're loyal, fun-loving and very affectionate. Just because they happened to get popular with Replicantes who aren't fit to be called humans, does not mean the dog itself is bad.
In terms of rescuing/buying, go with what you feel is best for you and your family. Just know that 1. there are plenty of full breeds at shelters and certainly through rescue groups if you don't want a mutt (I personally think they make the best pets, but that's just me), and 2. you can get a young dog from a rescue group that's already been house broken. Best of both worlds! Mine was 7 months old when I got her, and she was house trained, with all her shots and spayed. All for $350. And she's beyond awesome.
But please, please, whatever you do, do not buy a dog from a pet store. Please! Spend the extra cash and find a reputable breeder if you decide to purchase.
I'm off my soapbox now.