any dog has the potential to be friendly or ferocious, yes some breeds are more dominant than others and more powerful, but any dog in the RIGHT hands can be as calm as a lamb and i stress RIGHT hands.
If you a are a first time dog owner or inexperienced I would stay away from anything with a powerful past eg: pitties, presas, neos, bullies really anything that looks big and tough as these dogs are renowned for being a trying breed if in the wrong hands and potentially lethal if not handled correctly. (i know i have generalised and there are of course exceptions, but i'm talking of the rule not the exception, for an inexperienced owner)
also unless you are dedicated to being active everyday (regardless of weather or personal feelings) then stay away from high energy breeds (of any sizes) eg; Border collies, jack russells, setters, pointers, aussies, mainly the herding and larger of the gundogs (that being said, any of these breeds make great family dogs with ADEQUATE exercise and mental stimulation)
if you have not got good fencing, then stay away from hounds, or you will forever be chasing a dog chasing a woodland creature or pasting "lost beagle" signs all over your neighbourhood
unless you have a very good income, giant sized dogs are not for you. they may be some of the best family pets, but food, vet bills and general maintenance costs a lot for something that weighs more than you
what is your working life like? because many dogs require daily (sometimes bi-daily grooming to keep their coat in good health. if you are a busy person or are not interested in grooming than don't get a belgian shepherd, old english sheep dog or anything with long hair
where do you live? housing is very important, if you are a city dweller than something like a cattle dog or Aussie will not be suitable, where as a pug or Italian greyhound may be perfect. if you live in a more rural setting your choices will be less limited, but again a big yard does not mean that exercise is off the table.
what is your climate? obviously, unless your house is set up to be cool in the summer with air conditioning and the like and dogs are allowed inside the house than a spitz breed or northern breed should be not be considered for a hot climate. (and just because you have a dog with shorter hair does not rule air conditioning and cool shade out)
if you live in a climate that goes way below freezing every winter and you prefer outside dogs, than something like a whippet or greyhound would not be suitable. (but if you are not an Inuit who is actively involved is sledding and still believe in keeping dogs out at those temps, then you should be shot)
who will be living with the dog? if you have small children, perhaps a big bouncy dog is not the way to go (unless you are fully up to training and training and training) also many toy dogs are way too sensitive for tiny tots to be man handling them and can easily can injured. where as if you are elderly you need something sedate and willing to lay on your lap and potter around the house maybe taking a nice leisurely stroll around the block (exceptions of course)
what you have to realise is that all dogs need training, all dogs need exercise at their level of energy, every dog needs a lot of care and attention. so no matter what you get research, research, research. and don't forget if you choose to go to a shelter, pick a pup that will suit your homelife, there's no point rescuing an 120lb rottweiler if you own a flat and aren't home all day or a husky because it was cute but you have gout so can't walk much...really choose wisely and good luck
Really need to have more info on you and your home.
home (apt,single family,townhouse) own or rent..?
Do you work ? how long in a day will your dog be home alone ?
How much energy and exercise will you give your dog ? do you jog or do sports ?
How much training do you want to do ?
What is the weather like where you live ?
How much grooming do you want to do ?
How much shedding can you handle ?