I strongly prefer to have all personalities, so that means at least four of each gender, and I feel better when my town is gender-balanced. I dunno, I just have a thing for symmetry! I have 6 female villagers and 4 male right now, and while I like everyone in my town, it feels a bit "off" to me when there's a skew in either direction.
My favorite villagers are the ones I have the most nostalgic memories of and the strongest attachment to, and since my towns have always been pretty balanced, there's not much of a skew there either. My favorite villagers from past games are Antonio, Dora, Peewee, Tipper, Vesta, Lolly, Benjamin, Walt, Deli, Pashmina, Poppy, and Roscoe. In my current town, my favorites are Antonio (randomly got him when I started!), Sydney, Huck, and Bubbles.