I took the poll to mean out of
that specific list, which would be the best guard dogs. Not what are the best guarding breeds available. From that particular list, my opinion is that Rottweilers and GSDs are very good protection dogs. As far as guarding things where the human isn't around, just all by themselves guarding some junk yard, no, I don't think they're quite cut out for that. But for a family/house situation, those are formidable protection dogs. (generally speaking, of course) The Cane Corso and Bull Mastiff, I don't know that much about. I've read though, that the Cane Corso is a VERY good protection or guard dog. If you do a Google search and go to the breed clubs sites, read everything you can about the breeds you have in mind, that would also help you. And go to a show or someplace where there are lots of those dogs and talk to the owners....get a feel for them.
I agree that Pit Bulls probably aren't the best unless they bark at strangers. They seem to really like people a lot. Your protection type breeds have a tendency to have a healthy suspicion or aloofness toward strangers. Another good protection dog is the Doberman. But again, do your research and lots of it before getting any dog.
I voted for Rottweiler from your list. But remember, most of these dogs from the working group require an experienced, knowledgeable dog owner. They can be too much dog for someone who is new to dogs. And a poorly trained, poorly socialized Rottweiler is a ticking time bomb. And that goes for many breeds.
Personally, I think any dog that barks to alert the owner makes a fine watch dog. No, they may not be able to attack or back up their threat, but normally, bad guys are scared away by the attention a barking dog will cause. My Doberman is gone now and all I have are the Chihuahuas and let me tell you....they know how to bark. LOL. And I am well armed and know how to shoot.
So there you have it. No need for some bad guy to shoot or knife my dog as he goes for his throat. A lot of bad guys these days carry weapons and I wouldn't want my dog to get killed....won't do either of us any good. So, an electronic security system hooked up to the police and/or arming yourself, learning how to handle a gun, imo, is the best protection.