Not sure actually. We can't think of any of Mastiff type that doesn't slobber, but that isn't the same as
knowing there aren't. Fila Brasileiro is a type of Mastiff. It can top 200 lbs according to one site I found. It doesn't seem to be AKC registered (so what).
Rotts can get pretty slobbery when they get excited too. I got slimed pretty thoroughly last night when one of the 120lb. males jumped up on my couch to say hello.
GSD's (German Shepherd Dog) don't slobber, and are proven to be highly intelligent, intensely loyal and perfect for many uses besides herding such as police and protection work. As she said we're a little biased.
www.akc.org can show you the basic description and temperament of the dogs.
I'd google up a rescue group or club devoted to the breed you're interested in to get more info. For example, this site won't mention that Siberian Huskies absolutely can not be allowed off leash on less they are in a fenced in area. They will run. Great pyrannees will like to dig large holes in your yard. etc.
Like I said before, any dog can do protection work. A trainer in the chicago area trained a Golden Retriever just to show it could be done. Nice and happy one minute, ready to take your arm off the next. Big dogs can add a lot of intimidation factor, but shouldn't be a requirement. Another thing to keep in mind that the larger the dog is, the shorter it's lifespan. For instance Rotts and Great Danes average about 8 years or so. Proper diet ie. not kibble can extend that tho.