We have a 7 month old Staffy bull terier, we bought her from a add in our local paper, payed alot of money for her but came from a good home, we saw the mother and older brother and we were offered to see her dad who lived a few doors away.
This was the breeders 2nd litter from and the mother was a very laid back family pet.
I did'nt realy have a choice of puppies as Lily was the last bitch from the litter (she came from a litter of 8), she was a very full of beens puppy and still is. I would say don't pick the quite one but dont pick the hyper one either try and find a pup which seems bright and alert.
Lily took a while to settle in and hated being on her own, we bought her a cage to sleep in at night so she did'nt end up in our bed.
She's now house trained, still full of beens, very cheeky but very loving and my dd2 who has Autism has a special bond with her, she's now one of the family.
All i can say is be very careful who you buy from, make sure the puppy is healthy, wormed and make sure you see the pup with its mother, if you are worried get a vet to check the pup out before handing over any money.
Check your local dog rehomming centre, they may have pups looking for homes.