For the money, Pepper Foam is the best defense product out there. I have gone through 3 1/2 cans in the last 6 months. It sticks on their face and stops people in their tracks. Only downside is that most of it glows so if you around blacklight your hand will be glowing for a week or two. Its much better than the spray cuzz it doesnt get all around in the air and get you.
Stun guns are worthless unless you buy an expensive one.
Batons,Blackjacks,Sap's,Asp's are not legal unless you get a permit and go through a class, but are very effective.
Knuckles or Sap gloves are great but illegal.
Last but not least guns are the best but if you use one it carries a heavy price.