I've had several Rotties over the years. They are great dogs when properly trained . Like Rotjovi suggested, socializing them with all types of people and other dogs is crucial when they are young. I've done this with all mine and never had a mean one or a biter. They will still protect you and your family when needed although mostly by just their presence. They are very territorial and will protect the home as well. They are great dogs and good family dogs. My kids were 1 and 8 when we got the first one, now on our 4th. There is also lots of good information out there for help in raining and training.
Hope this helps.