I met a woman at a rare dogs show who raised Fila's. She would not let any stranger near them. I beleive this is her failure not the failure of the breed, however I would caution you against getting yourself into an agressive breed like a Fila or canario unless you're determined to train one.
Another Mastiff option would be the Neopolitian mastiff. I did a ton of research before I got mine, and I beleive them to be the best combo of guard instinct without the dangerous agression. It's hard to find really good pictures. I have an 8 month old Neo. She looks like an overgrown cross between a black lab and a Weimeriner. Check out
www.neorescue.org
<img href="http://neorescue.org/images/newtopcorner.jpg">