I wish I could tell you how many people told us that "he's gonna eat your face off!"
What we DID get was a wonderfully tempered, sweet-natured, devoted Velcro dog who insisted upon accompanying us to the loo. The males are especially loving and endearing. Our first was Pets On Wheels dog who visited nursing homes - to the delight of the male patients who were thrilled that he was not just another "little fag dog". As for being a Watch Dog, this is not a 'barky' breed. Quite the opposite, in fact. If you want a "watch dog", your small terriers are better.
What you WILL get is a Guard Dog. This breed is naturally protective. They will interpose themselves between you and a stranger - often leaning against you leg in order to sense how uptight you are. Subtle. They take their cue from you. They like who you like.
As for being family dogs, mine are wonderful. My 18 m.o. grandson has been a terror: punching and twisting ears, stump pulling and other contrived horrors. Mostly my three run and hide from him. Our big male has learned that if he licks the baby's face, he is left alone. Dog, one; baby, zero.
These are highly intelligent animals who learn extremely quickly and want to please. They are exceedingly social and cannot be isolated, kept outside or chained. THEY NEED THEIR PEOPLE.
Because of their intelligence and inherent protectiveness, Dobes require that YOU be in charge or else THEY will be. As we found out, there is no place too warm, too soft, too cozy for a Dobe. They will take over your bed, your sofa, your comfy chair. And, they do not like men with hats, carrying things or raising their hands up in menacing gestures. But, that's their job.
It is said that once you own a Dobermann, you will never want any other breed. It's true. Oh, it's true.
If you're an experienced dog owner and can choose 'em at 6-8 weeks, get whatever you like. Otherwise, though I would avoid the Dobe.
There are some very knowledgeable Dobe owners on this thread, and a good Dobe is a wonderful dog. But there are some very aggressive and some very neurotic bloodlines out there (some dogs are both). My mechanic had three that were wonderful dogs and gentle as lambs, but the last couple of examples I've seen have been highly nervous and neurotic, and I wouldn't recommend them for kids. One was a washout in the obedience qualifying class for our agility center - he just simply would not obey his owners and kept growling and snapping at the other dogs. (His owners were a couple of granola types, though, and it was clear they weren't in charge. He was still much too nervous to have around kids though.)
One of our neighbors has a Chessie and she's a nice dog, they have two little kids. Don't know much about the breed as a whole.
We have a Lab, and we love her. If you have tiny, tiny babies, a Lab may be too boisterous and rough, especially as a puppy. But they are friendly, tough as leather, and the kids can't wear them out. They are not guard or watch dogs as a breed, but our Lab is very protective of the children and will interpose herself between them and strangers (this may be of course so that she can jump up and lick the stranger's face first!)