I do prefer all dogs myself. I really love the designs of the dogs, and I love the dogs in real life. More specifically I love the lazy dogs. Biskit, Walker, Bones, Lucky, Marcel, and Benjamin.
I have an all ducks town and a ~whichever villagers i feel like~ town. I usually don't like towns that have 3+ of the same species, unless it's their theme (all cats, all wolves, whateva)
I used to have a real thing for pairs of animals, it was seriously hindering my enjoyment of this game. If I wanted all the personalities I was very limited on who I could pick to live in my village. If I wanted Phoebe, I would have to pick another ostrich. If I wanted Sylvana, I needed another squirrel. I think this stemmed from wanting Chrissy, but also wanting Francine as they are sisters. So I had 2 rabbits living next to each other, and the rest being random animals seemed off to me.
I've since gotten over this, now I'm the complete opposite. I accidentally moved in pashmina, forgetting chevre is also a goat. Though I think I'll let pashmina stay as I had a very hard time deciding on an uchi type that would fit my town, and chevre is way too cute and close to my heart to get rid of.
I used to have two of some species, but just when they look different like Fauna and Erik, but now i prefer Variety in species so i can meet every of them.
I have all different villagers except for two elephants, Dizzy and Tia. I'm partial to keeping them both because I think they make a cute "couple" Aside from that, though, I generally tend to value having a variety of species. I have a wolf, a rabbit, a chicken, a rhino, a horse, a cat, an alligator, and a mouse.