Although some breeds possess traits, and soft natures that make them more "likely" to be submissive and friendly with all and sundry eg: Labradors.
And others have traits and harder natures which make them more aloof in how they view strangers .eg: A GSD or Doberman.
Its basically down to the dogs individual genetic make-up, its socialisation when a puppy, along with its confidence level, as to how they react to strangers.
There ARE Labradors that are very aggressive (often from fear) to strangers and that is not typical of the breed usually and indicates bad breeding.
Also there are GSD`s that welcome all strangers as their best friend. Again its not typical of the breed. A GSD should be initially wary about strangers but fully accept them if its owner does.
So....to answer your question. Well that all depends on what you mean by Nice and not nice, which I interpret as aggressive.
So its True, some breeds on "average" are automatically "nice" to strangers and some breeds tend not to be so nice.
The best sort of dog is one that ignores strangers unless there is very good cause to be "not nice" towards them.
GSD owner for 56 years. (UK)