I currently have the opportunity to work with a Dutch man who specializes in selecting, breeding and training dogs for military, police, SAR, etc. He has been in the business for a long time and has placed many dogs in places such as Boston PD and Iraq.
When I saw this thread I asked him what he thought of the Presa and the other giganto "protection" breeds.
His words, "they are nothing." Why i asked? "They are like a balloon, one big bite and pffft nothing left". Remember that working dogs are trained with DRIVE. That is prey drive.
This man likes Belgian/Dutch Shepherds and Eastern European German Shepherds. He doesn't think much of the others, however he has shown me video of a pretty good Beauvier. He said he would rather have a Doberman than any of the big ones like the Presa.
Why? Look at video of working dogs. Some dogs can bite through obstacles better than others. For instance, jumping through a hoop with streamers to deliver a bite or jumping through a switch smacking them on the face. Many tough dogs will flinch and not bite properly when faced with this. Only a certain few dogs will truly have the stuff to make the bite with good form.
This guy trains KNPV, not Schutzhund, he has little respect for the sport of Schutzhund compared to KNPV. For those that don't know, KNPV is Dutch police dog training.
When it comes to protection I want a trained dog that I know will do what I want. Not a dog that has the physical traits, and I have to hope that protection instincts will kick in because even then he won't be as effective as the trained dog of lesser build.