In a shelter, especially with puppies, you're probably going to end up finding mostly mixed-breeds. In many shelter cases, though, the lineages of the litters are educated guesses. It's often unknown (and hard to figure out) what the parents are when puppies come in to a shelter, or sometimes they'll know the breed of one parent, etc. So, it's kind of a crapshoot as to how big the dog will grow up to be, which I'd assume is a consideration in a small apartment. With such unclear backgrounds, it's also hard to guess what the dog's disposition is likely to be, too. Something to keep in mind, I guess. While I do very much advocate adopting from a shelter, you may be better off getting a dog that's at least a year old if you're going to take that route.
A work of art is an invitation to love.