Well, I have a golden retriever whose enthusiasm for anything humanoid knows no bounds. She would be delighted if Attila the Hun suddenly appeared in the living room and wanted to pet her.
Having said that, if I wake her up by sitting next to her on the sofa (yes, she claims the furniture) and patting her, she will lift a weary head and look at me. That's all, just look at me. I can hear her brain saying, "Would you kindly leave that until I don't feel like sleeping?"
Other dogs in my extended family aren't that easy going. We've had ones who are fine with family and friends but can't even be approached by strangers until after the owner greets the person. My sister had a dog who would growl at anyone except her if he didn't feel like being touched.
I think it depends entirely on what type of personality you want your dog to have. It can be friendly, stand-offish, unfriendly, or anywhere in between. If you're thinking of a particular breed, that might make a difference. Retrievers tend to be friendly, guard dogs like dobermans or shepherds are usually more reserved. We had dachshunds when I was growing up; they were yappy and would nip if someone they didn't know put their hands near their mouth before they'd calmed down; not a family member, but a stranger or even a neighbor.
If you have a mixed breed, you can probably make them have any personality you want.