As long as we are talking dogs here, let me say a good word for my dog breed. PUGS. They are absolutely the most loving, smartest dogs. Now, ages ago, my mom raised miniature poodles, also for awhile Pekingnese. And at one time we had a little terrier of some kind, she called him a "rat terrier". He was good, but a bit rambunctious. These pugs are something else. We had one that was given to us by a neighbor. She lived 14 years, and would probably have made it longer, but we did not have her spayed. That is something you have to do with these dogs, as they are prone to uterine problems. (We never bred her either) The current pug, which my husband insisted on getting too short a time after our Suki died, is the Queen of the House now. The pugs, as you know are mostly small, ours weighs 20 pounds. The are not hot weather dogs because of the short muzzle, and heat nearly killed our first one as we didn't know that! The one drawback is "dog hair" ...you'd think a short-haired dog would not have much to shed. But they shed big time. And the hairs are like porcupine quills, and stick into furniture upholstery, carpet, clothing. I've bought all the gadgets that claim to remove dog hair, but they don't work in this case!
The Pug is a wonderfully smart dog, ours can learn most anything, although we've not had her formally trained. She will lie in the living room, and watch the wall clock until it's feeding time, then come and stare at me until I get up and prep her meal! She doesn't snap or bite, gets along great with all people (good watchdog, but will lick the visitors to death after she's finished barking at the them!) We've not had cats around her, but I'm sure a young pug would adapt quickly. Ours is now old enough that she is stand-offish with other dogs. About the spaying, this one was acting sickly and dragging around, and when we took her to the vet and had her spayed, she became almost a puppy again. Running around, playing with her dog toys...a totally different dog. Anyway, this is my recommendation for dog for small apt. if you don't mind the hair. Also, Boston Terriers are great, without the massive hair shedding! (My mom also raised those for awhile).