well, lets see.. as an old woman who's lived with all kinds of dogs.. here goes.
pit bulls are ONLY aggressive towards other animals, they will NOT protect possesions or human beings. a well bred pit bull will help the thieves carry your stuff out and lick their faces when they are done.. lol
GSD's are great protection dogs, but as others have already pointed out, they NEED a job. and just hanging out in the yard or with your wife is not enough of a job. if they are not stimulated and engaged they will go nuts and destroy things. i know of one who ate the entire side of his owner's house, pulled the siding and wallboard off the side of the house.
rotts were bred to be war dogs originally, they are excellent property protection dogs. And great couch potatoes too. the downside is that they don't live long, most don't make it past 8 years, lucky ones make it to 10 and 12 years is extraordinary.
Akitas are my favorite all around dog. they are loyal, almost to a fault, great with family and kids. they are very quiet, they only bark when there is a reason, and most of them have a kinda howl-talk thing and they try to imitate words. a friend's akita used to howl "iloveyou" when they came home.. akitas are social dogs though, they don't take well to being left alone for long periods. they need to be part of the family. a well bonded akita will protect it's family with it's life and never ask for anything more than a hug and a pat on the head.
fair warning though, none of these dogs train themselves, and if you've never owned a dog before you WILL need help to learn how to train them. do not assume, that just because you are human you automatically know how to train a dog. and none of these dogs is an ideal dog for a person who has never owned a dog before.
actually, any large dog (60 lbs or larger) will be an excellent deterant. most non-dog people are afraid of dogs that are bigger than a cat. which opens up all kinds of possibilities. there are american bulldogs that are all bluster and not too bright, there are mastiffs that are huge but are excellent couch potatoes and gentle giants. there are newfoundlands and st. bernards that are excellent companions and family dog and have a HUGE bark. there are irish wolfhounds that are the tallest domesticated dogs in existance, that are wonderful family members and again, gentle giants with a BIG voice.
one other caution and word of advise. dogs are NOT weapons, they are companions and family members. if protection is your aim, a dog is a poor choice. they are at best, a good deterant. i know that no one tries to break into my house, because the ignorant people that try to break into average folks' homes are afraid of dogs. we've had bad people come to the window, or in the back yard, but none has made it past getting their head inside to see one or more of the dogs staring at them.. then they beat a hasty retreat.
but if a thief is prepared to deal with a dog the dog isn't going to win. that is simple fact.