I wouldn't have any of them. For starters, the liability with them is too high, and your insurance company can pull your policy - regardless of how well you take care of the dogs.

You want a good guard dog? Great Pyrenees. They are VERY large dogs, rather formiddable looking to strangers, yet docile enough to not have to worry about your neighbours kid wandering into your yard. They do bark quite a bit at night. However, that is how a would be thief will know first hand that they are there. If they are STILL stupid enough to go in the yard, they WILL be greeted by a HUGE white mass running towards them at full speed. They typical pyr will weign in at least 100 pounds, so they have some power behind a protective response. I sleep very well at night with my Pyr in the back yard, and am looking at getting another one, which will be housebroken and trained, so he can stay in the house.