IMO show line BC would work well for you. But remember, your position as pack leader is to protect your dog, not the other way around. No dog should ever attack unbidden, unless home alone. If you want a dog to bark, growl or lunge at people it is downright dangerous to have a dog that makes this decision on it's own.
If you want a dog for a family protection or protection reason, pay the money to do the training with your dog (don't send your dog away to be trained) and make sure that you FULLY understand the laws and ramifications of your dog biting anyone. There is a lot involved.
On a side note, how many people have 'Beware of the dog sign' or similar? Did you know that by having that sign you are liable automatically if someone goes into your yard without permission and gets bitten? Sorry for going OT