There are good dogs and bad dogs of any breed. I have had dogs all my life and my third dog was a Staffordshire Bull Terrier. He (Jasper) came from a rescue home and he turned out to be one of the best dogs I have known.
Jasper was strong and muscular, but had a very affectionate nature. Totally not aggressive. He had quite a dominant character sometimes but never violent. I only ever saw him bite once in anger and that was someone who was physically threatening me, and after a series of growls and body-language warnings. I had also been defending myself and was clearly distressed. That's the only time he ever bit anyone.
I wrote an article for a local magazine about Staffies (Jasper was something of a minor local celebrity during his lifetime) and also found, to echo what the Kennel Club says, that they are good with children. In fact, an historic nickname for the breed is apparently "the nanny dog". I believe this stems from the days when poor families would keep a Staffy for ratting and fighting (a bit of extra income could be made from both). The dogs were bred for fighting, but with a gentle enough temperament so that they would not turn on their human owners and could reasonably safely be pulled away from each other by the fight's referee. Often (according to records I found) the injured dog would be transported home in the pram/cart WITH the owner-family's latest baby. Also, the dog was sometimes fed before the children (the reasoning being presumably that the dog brought in a bit of extra money and was therefore further up the hierarchy. Times were hard and quite brutal).
Jasper was very fond of children. In fact, he appeared in several different stage productions of the musical Oliver!, playing Bill Sykes' dog Bullseye. He was a great favourite with the children in each cast and would happily sit and play with them backstage. I never had any qualms about him being with the children, even in such a lively and excitable situation. He was also always very happy and patient with the children and any others who wanted to meet him at the Stage Door afterwards.
When I used to work in a rural location, Jasper would often accompany me to work and was always well behaved with colleagues and visitors. On days when he couldn't come in, he went and spent the day with an elderly neighbour, who adored him, He was always gentle with her and always safe when she took him for his walks.
There was also a situation in which I found myself in some danger whilst walking on Dartmoor with Jasper. It's true to say that he actually saved my life, by doing a bit of a "Lassie" and running off to find some nearby Norwegian walkers and bringing them back to where I was to help me. But that's a bit out of the ordinary.
Sadly, Jasper passed away from cancer when he was 12. The dog I have now is a Jack Russell, but I would certainly not ever hesitate to have a Staffordshire Bull Terrier again.
Unfortunately, I did get a fair few instances when I was out and about with Jasper of strangers telling me "that dog should be shot", "dogs like that deserve a bullet in the brain", "I don't understand why people have 'that sort' of dog", totally unsolicited and not in reaction to anything he was doing. I was always mindful that he was a strong dog and that not everyone likes dogs, so he was always on the lead when walking or under close control in the park. Those unsolicited comments were quite hurtful and upsetting.
I'm very sorry to hear about your friend, that must have been very distressing for her. But even the sweetest natured dog might bite. The dog probably bit her because it was unwell, in pain or afraid and not purely and simply because of its breed.
Sorry for the long post - but I hope at least some of it is helpful. I wish you well with whatever dog comes to share your home. And I can honestly say that I was someone who never wanted to have a Staffordshire Bull Terrier. Circumstances sent him my way and I was glad that I was proved wrong. I've tried to attach a picture of Jasper out and about on Dartmoor (never tried putting a picture on MN before, so hope it works).
Very happy to answer any other questions you might have - and I promise to answer them objectively. I totally get why some people are hesitant about this breed. Best wishes to you. x