I recommend a prong collar-sometimes called a pinch collar. It looks terrible, but when you try it on your arm you can see that all it does is squeeze the neck. You must fit it properly. See this web-site:
How to fit a Prong Collar The Atlanta Dog Whisperer uses this method for all dogs. It really does work along with a stern "no pulling" command. Be sure you have a nice leather leash, no cheap retractable leashes. Keep your dog close to you and have it walk beside you, not way out in front. Staffies do pull more than other dogs--this collar is what you need.