Deer and Horses are definitely my favorites out of the existing villagers, two of my dreamies are horses but there isn't a deer design I really dislike!
As in for villager species I would love to see, I have a few! Even if they're just model variants, I would love to see Lop earred rabbits, different dog models to maybe make longer furred dogs, or maybe even longer furred cats (I would LOVE a ragdoll cat villager). For more species themselves, maybe bats? I would love to see some insectoid/arachnoid characters! I've seen people make really cute tarantula villagers on twitter and deviantart, so things like a beetle villager would be really cute to me! or even more aquatic villagers, that would be really neat since we already have a few octopi
I don't really like the idea of fish or insects as villagers. The fact that you can catch their brothers and sisters around town and keep them in a cage or bowl just make the whole idea of them as villagers...awkward.
This is already the case with octopus villagers.
Like everybody else said, bats and moths. But also, some variation in the dog villagers would be nice! Like, they look different depending on what breed they are, like Booker and Cooper. Also, cryptid villagers would be DOPE. I want a Fresno Nightcrawler neighbour!
We. Need. Turtles. Or tortoises, same difference. The only ones we have seen are Tortimer, Kapp'n, and the gang on the island in ACNL. None of these are actual villagers, however. We need em. Also, we need bats as well, as everyone has already mentioned.
To me it seems that Nintendo is kind of conservative when it comes to which species they include in Animal Crossing(with the exception of the octopus villagers).For New Leaf they added hamsters and deer,both fairly common and well known species with the kind of limbs that make it easier to translate them into something anthropomorphic so I doubt we'll see any bug,snake or fish villagers added to the game.I've wondered why the game has bear cubs and adult bears but not puppies and adult dogs,kittens and adult cats,ducklings and adult ducks,etc.I'd like to see the younger versions of some other species included as villagers.I like the Geico gecko and I think Nintendo could make a gecko into an interesting villager(if they don't get sued by Geico for some sort of copyright infringement).