I like have more than one of the same species in my town, but not all the same. My plan right now is to have 2 deer, 2 ostrichs, 2 dogs, 2 cats and 2 bear cubs!
I like my town to be diverse, but I don't care if I two or three of the same animal in my town for a bit. As long as there's a balance of males and females and personalities, I'm happy. lol
Definitely diversity. I don't like having more than 2 of any species in one town. Feldspar has 10 villagers and 9 species (with my two sheep being the doubles).
I tend to have multiples of the same species. I like it that way, it's cute when they interact with each other. But in my main town, I don't necessarily aim for it, it just sort of played out that way. When I got my wolves, it wasn't my intention to get them because they were the same species, I just wanted them for nostalgia. I also used to have 2 cats at once (Mitzi/Ankha were my starters). And I almost had 2 gorillas at the same time until one moved out unexpectedly.
I'm a fan of having a diverse group of villagers, but if some of my dream villagers share a species I'm fine with doubling up. One of my towns is actually a bird town, but it's not exclusively the actual Bird species. It features two birds, a chicken, a duck, an eagle, four ostriches, and a penguin.
I do like having different species, genders don't bother me though. I would probably have a whole male town and be happy with that. I do like a few of the girls and I have my favourites now.
I would have actually liked to have had 10 villagers of different species though. Just didn't work out