Is a Giant Schnauzer a good watch dog?

I have owned an American Bulldog, GSD and I now own a APBT. However, The APBT has gotten such a bad rep. that I'm really skeptical about ever purchasing another one. Mine is an extremely well mannered dogs and spoiled rotten! I love the look of Giants and from what I've researched, Giants make great watch dogs as well as a family companion. Any thoughts?