1) ... I love dogs, and really want one
2) ... so I can have a companion living on my own.
3) ... I want a larger dog, and I really like the Bullmastiff, but to be honest I'm not sure if I would like to own SUCH a large dog.
4) ...I know the pros and cons of each,
5) ... and I'm going to train him myself.
I'll try to keep this brief; aside from the good advice already given:
1) Sorry ... but I have serious reservations about anyone posting on
"First Time Dog Owner and Basic Questions", getting one of these powerful breeds.
"Loving dogs" and
"really wanting one" does not, in and of itself, qualify you to be a confident and competent owner of a Bull Mastiff or AmStaff. Having said that, either breed is a wonderful choice for the right owner.
2) I'm not suggesting that you didn't do your homework, but if simple companionship is what you're primarily looking for, there are a myriad of other breeds which might be more suitable for
your needs.
3) Aside from the additional expense of owning a larger dog, size is less of an issue than your ability to raise, train, handle and provide for the needs of the particular dog you get. Larger dogs, IMHO,
tend to be easier to train and handle than small breeds. For a first time dog owner, it might be best to look to softer breed than the ones you've zero'd in on. There are many large dogs which would make ideal companions for a less experienced owner. Again, this is just my opinion.
4) "Knowing the pros and cons" of a particular breed
on paper, is oftentimes quite different from the reality of "ownership". This is why there are so many beautiful Dalmations, Pit Bulls, JRT's etc, etc, etc, which end up abandoned in shelters and/or euthanized.
5) It's not that you
couldn't train one of these dogs yourself, but raising and training one of these powerful breeds takes more time and know-how than a softer breed,
especially when it comes to their needs for ongoing and extensive socialization.
There are far too many people who have purchased the "breed of their dreams", only to end up in a canine nightmare. I would respectfully suggest that you seriously rethink your personality, experience, lifestyle and finances, to best determine what qualities you would ideally like to see in your dog. If we were to speak in person, the first questions I'd ask you are: "Why these particular breeds?" and "What is it about these particular breeds you really like?" Somewhere out there is
the perfect first dog for you; I simply question if it's an AmStaff or Bull Mastiff.
Most of those online, breed-choosing web sites are fun, but fairly useless. But if you were to (re)post your inquiry on this web site, I bet you'd get some great input as to breed selection.
Again, this is all just my opinion. Best of luck!!!