1 Watchdog Ability: Both the Bullmastiff and Mastiff are great watchdogs. These dogs will bark and alert their owners when an intruder is present.  Adaptability: The Mastiff has better adaptability.
http://dogs.petbreeds.com/compare/41-101/Bullmastiff-vs-Mastiff
Prevalence: Common. The mastiff is truly a giant among dogs. Full grown, males start at 30 inches tall and can weigh as much as 200 pounds (90 kilograms). Females start from about 27 inches in height and weigh around 150 pounds (68 kilograms). The mastiff is massive, powerful and muscular.
http://www.hillspet.com/en/us/dog-breeds/mastiff
The Old English Mastiff is a massive dog. The Mastiff has a large, heavy, square head with a well-marked stop between the eyes. The muzzle should be half the length of the skull. The medium-sized brown to dark hazel eyes are set wide apart with a black mask around them. The nose is dark in color.
https://www.dogbreedinfo.com/mastiff.htm
1 Exercise Needs: Both the Bullmastiff and Mastiff will require light exercise. Not much exercise is required to keep these dogs in shape. Owners who are frequently away or busy might find these breeds suitable for their lifestyle.  With Kids: Both the Bullmastiff and Mastiff are good with kids.
http://dogs.petbreeds.com/compare/41-101/Bullmastiff-vs-Mastiff
1 Kumaon Mastiff, a rare breed of dog originating in India. 2  Neapolitan Mastiff or Italian Mastiff, a breed from Naples, Italy. 3  Pakistani Mastiff, the Bully Kutta, from Punjab.  Persian Mastiff, also known as Persian Mastiff and Iranian Mastiff is a breed of livestock guardian dog indigenous to north of Iran.
https://en.wikipedia.org/wiki/Mastiff
However, the breed is not recommended for toddlers because of its great size. The mastiff's guard dog roots are likely to manifest themselves when visitors come to the home. The dog tends to be suspicious of strangers and protective of his family and perceived territory. Even so, the mastiff barks infrequently.
http://www.hillspet.com/en/us/dog-breeds/mastiff
1 Training: Both the Bullmastiff and Mastiff will be hard to train and will be difficult for first-time owners. Owners will need patience and perseverance to train these dogs and might need to seek out obedience schools.  Watchdog Ability: Both the Bullmastiff and Mastiff are great watchdogs.
http://dogs.petbreeds.com/compare/41-101/Bullmastiff-vs-Mastiff
The confusion between the mastiff breed and the mastiff family makes it very difficult to trace the history of the breed. Even though the mastiff family is one of the oldest and most influential, the breed is undoubtedly of more recent, though still ancient, origin. By the time of Caesar, mastiffs were used as war dogs and gladiators.
http://www.animalplanet.com/breed-selector/dog-breeds/working/mastiff.html
Mastiff means a large molosser dog. The term the Mastiff group or the Mastiff has been used synonymously with the term molosser. For example, the bulldog breeds, the Great Dane, the mountain dogs, the pit bulls and even smaller dogs such as the Boston terrier, may be considered Mastiff in this broad sense. 1 List of Mastiff breeds.
https://en.wikipedia.org/wiki/Mastiff
The Mastiff is a very massive, powerful, muscular dog. Dominance levels vary, even within the same litter, but it is often called a gentle giant. A born guard dog, the Mastiff rarely barks, but it is in its nature to defend its territory and family, and is more a silent guard rather than a barker. When an intruder is caught the dog is more likely to hold them at bay, either by trapping them in a corner or lying on top of them rather than an all-out attack.
https://www.dogbreedinfo.com/mastiff.htm
what is a mastiff
A mastiff is a very massive, powerful, muscular dog. Mastiff is a very massive, powerful and muscular dog.