Staffordshire Terriers are WONDERFUL.
I was thinking the same thing. Staffordshire or Pit Bull Terrier can make wonderful family pets.
Two things the OP would have to consider:
Barking- Most of the other suggestions have been dogs that bark a lot. So if that's what you're looking for this would probably not be the right type of dog since most do not bark much. For me, that's a huge plus. Dogs that make a lot of noise drive me crazy and I would not have the patience for that at all. I suppose it's a "warning" but I would only want a verbal warning if there was a true danger, not barking at every person/thing that goes by. I have only ever heard my dog really bark twice and both were times that she felt we were being sufficiently threatened. That said, the bark/growl is very intimidating. (More so than much larger dogs I have been around.)
Other dogs- Many are not good with other dogs. You would either need to get a puppy and socialize it with your other dog early on or adopt an adult dog that has proven to be great with dogs. Our dog is very fearful/aggressive with other dogs. We know she was attacked because she has many bite scars (mostly on her face), but dog aggression is a common trait with the breed regardless of their life experiences. This has required a huge time investment in training/socializing, but she is truly the perfect pet in every other aspect: wonderful with my kids (9-16), obedient/quick learner, quiet, never any destructive incidents/behaviors like chewing, "potty" accidents, etc.
Also, not specific to this breed, but everyone should call their insurance company prior to bringing home any new dog. I had read through our policy and there was no mention of dogs, but I still made DH call before we adopted our dog. They provided us with the following list: "vicious dogs including Akitas, American Bulldogs, Beaucerons, Caucasian Mountain Dogs, Chows, Doberman Pinschers, German Shepherds, Great Danes, Pit Bulls, Rottweilers, Staffordshire Terriers, Wolf Hybrids, or any mix thereof" We had to change our insurance company and would never have imagined how difficult it was to find something that did not have any breed restrictions.