I've had many dogs over the years. Almost all of them have been indoor/outdoor dogs (out all day in all night) so apartment dogs are an alien concept to me, but I'll add what I can.
Our collie was easy in the house and not too demanding wrt exercise. He was friendly up to the point someone reached for the door when we weren't home and then he moved to block and backed them off of the patio. He would sound whenever a strange vehicle came down the road and would announce unfamiliar people with a yipping bark. If inside he'd yip/whuff upon noticing a strange noise and growel if it were a stranger approaching the door. He kept my sister and I in the yard so well that my mother let him baby sit us outside. There is no question that he would have died to protect any of us from harm, but would be the perfect gentleman if the situation was friendly.
My aunt had boxers and I had a white one from one of the litters. He was very energetic, but was comfortable flopped around the house. He would take your arm in his mouth and lead you around by it without harming you in any way. As has been said he would stand between you and any perceive possible threat. He didn't announce strangers by barking, but instead would jump up and stand with ears pricked forward and then run to the window to look out. If it was someone he knew he would whine and wiggle. Strangers got a whuff? and men got a low growel if they approached the house.
The english sheep dog barked at anything that moved that wasn't family. He'd growel if he was in the house, but stood "guard" on the porch quietly if anyone approached.
I had a malimute female that was marvelous. Followed voice commands, friendly but slightly aloof, walked on lead perfectly and a bit of a clown. She had her own dog, an ancient female lab, that was the sweetest animal I've ever seen (as almost all female labs I've had around were). The malimute was the only dog I've ever had that there was no doubt that she would tear someone apart if told to or if HER people were threatened. She was not overtly aggressive, but I introduced her to everyone that might come into the house or on the property beyond deliveries/meter reading. She's the only dog I ever used in a situation where I was uncertain of other people and she certainly intimidated three young men into leaving the property in a hurry.
Labs and goldens, I can't say enough good things about them! Great dogs, not demanding, always glad to see you. They've barked to announce strangers and groweled when they approached the door without being introduced. Our old guy has gotten on in years, but he still alerts when a car comes up the driveway or someone comes on the porch. I've only heard him growel at a person once and that was when a stranger friend of my son pulled up to the kitchen door and just walked in the door. I had to grab Sampson before he got past me and to this dumb teenager and the big yellow dog still wanted to find out what the pale kid tasted like until I told him ot wait outside.
I've had little dogs that were more inside critters. My sister's cocapoo is the sweetest thing, but lets us know if anyone even sets foot on the property and will growel like a bear if she's inside and someone she doesn't know comes towards the door. She won't back down for any dog and sometimes is stupid about it. Out fox terrier is usually quiet, but whuffs? to let us know someone is near the door. Otherwise she's almost always silent. She sleeps with our daughter or on the stairs and I watched her jump up and bristle and give a surprisingly low growel when a boisterous friend of our came over for a visit one night. She's suspicious around strangers. We had a shepard/hound mix that was smarter than I am (but was kind enough not to rub it in) that would whuff? at any property boundary intrusion, growel if a stranger was within 20 feet of the door, and was completely silent and manouvered to get behind anyone that wasn't greeted as a friend that he hadn't been introduced to. He was protective and actually bit a fellow on the calf that was poking around the house looking for us when we weren't home. He said that the dog had kept him in his car for a while standing between him and the door and pacing back and forth ateranately whuffing? and groweling. Being stupid he got out anyway and the dog peeled off of the door and went around the side of the house and he thought he had been all bluff, silly him. The moment he was closer to the door than the car the dog came streaking from around the bumper of his car and hit him from behind without a sound. The bite was just a warning as it didn't break the skin, but left a large bruise (I know it was a warning because I watched this dog chew 3 inch oak tree limbs into dust all the time for fun).
