I can only go by my own Stafford girl Grace (BYB) and various other I have known throughout my life. They are a very popular breed in Australia.
I would describe them as confident, playful, fairly active, spunky, and very affectionate. They love their people. Actually, they love all people.
Despite being on the small size, they are very strong. They need training from day one, because a strong, playful, over-friendly dog without manners is not exactly fun to be around. A Stafford with manners is delightful.
They do seem to have an affinity with children. It goes without saying that they should be supervised and trained from day one as they can be very rough players and can inadvertently hurt a child (or anyone really, see manners above!)
They are intelligent dogs and the ones I have met are very calm, confident individuals except for the excitement upon meeting another person or playing a game. But still a very confident breed.
They definitely need exercise and they definitely need to be a part of the family. I remember adolescence was interesting with Grace whilst we figured out her exercise needs (she did destroy a door during this period, but she also had mild separation anxiety which we nipped in the bud straight away and now she is 100% trustworthy to leave loose in the house and yard.)
At 11 years young, she is still playful, always up for a game and a cuddle. Very tolerant with my Abby, who is a very playful dog herself. She still does dumb things that make me laugh (think dog who never quite grew up) but I wouldn't have her any other way. I would say that they tend to mature late and in a lot of respects, not at all lol. Although they are playful and need their exercise, I wouldn't call them a hyper or 'up' dog. The ones I know spend most of the day doing absolutely nothing. You come home, do some exercise together and they are quite happy to vege out on the couch for the rest of the evening.
On thing about Grace is that she loves other dogs. She isn't allowed to play with many other dogs, just her small circle of friends because they match her play style and she can be a little rough for others. Funnily enough she is very gentle with small dogs and puppies and the best thing we ever did for Grace was get Abby when she was 5 years old. She fell in love with that puppy and has been ever since.
Having said that, Staffords can be predisposed to DA so if you want a dog park dog or a dog that has a low chance of exhibiting DA, maybe don't choose a Stafford.
Because I've my not so good experience with Abby (Chi x) I'm pretty determined to get a dog that is socially confident and not DA. Everything else about the Stafford is perfect for me. I dabble in obedience/agility and whatever other sports take our fancy so I'd be happy with a Stafford... in fact I think it could be a LOT of fun! But I'm not sure I want to risk DA again...