I look for weird, tiny aesthetic things in my maps. For example, I LOVE triangle grass, circle grass is good, but if the town has square grass: bye-bye, I'm out the door. I feel like the grass pattern really sets the feel for a town. Square makes a town seem larger and wider and spacious, and that's just something I donrt want to feel like. Circle feels neutral in all aspects, it's a nice medium. Triangle feels cozy and close knit and detailed: there looks like there's soooo many more shapes on the ground in a Triangle grass village. Ironically, I believe both my towns have circle.
I also look at the color of the train station. I hate the green train station, and if the town has it, I can't do it. With my town called Blueplum, I wanted a blue train station for obvious reasons and so I looked until I got one. I love the red station the most because it matches the top of the bulletin board, and the brown the second because it looks town-y and sweet and its just classy.
Town hall color is pretty important for me, too. I don't like the plain town hall, the one that is colored exactly like AC:CF town halls. I think the blue and green ones are good, but my absolute favorite by FAR is the yellow town hall with the green roof. So pretty.
Fruit is also important to me. I love apples. I like cherries and peaches. Pears are cool too. I am not a fan of oranges, however. In real life, OR in the game.
Neighbors are huge. I don't mean I have to have popular villagers, I mean I personally have to like them, at least if just only a little. This is a priority for me because I love to make me villagers, all of my villagers, stay in my town for a loooong time. I like getting all villagers (that I've had) pictures and enjoy my time with them.
And lastly, I do look at the layout, but I usually don't judge too much while on the train with Rover. A town may "look" like it doesn't fit your taste upon first glance, but once you visit it you may see that it actually FEELS just right when you walk around. I look for spread out buildings and the right feel.