My dreamies are mainly looks. One of my dreamies, Ankha, I love her for her looks, but also because I love anything to do with egyptians and ancient Egypt.
I'm going to list the dreamies I actually sought out/am seeking out; the rest of my dreamies moved in randomly. xD
Diana - I love her color scheme, and deer are one of my favorite species!
Apple - I'd never had a hamster in AC before Apple, and I find her really cute.
Apollo - I love eagle villagers!
Skye - I love her design, and wolf villagers in general.
Filbert - I had him in Wild World, and he was one of my best friends there!
Mira - She's one of the only Uchi villagers I like.
If you look on the villager trading plaza there is a villaget popularaty thread but it's based on look and popularity! Like Rosie in the movie looks cute and she's in a movie!
I have currently five cat villagers and at least one more someday because I really love them. I looked at all the cat villagers and then decided which ones I would love to have in my town. At first I wanted an all cat town but... I began to like the smug personality too much... so... currently not happening.
Marshal - At first I wanted Kyle as my smug but I sadly had to let him go (and I'm too lazy to cycle through 16 villagers). Then I looked at a list of all smug villagers and which one I would love to have and Marshal was one of them. I love the AC squirrels and his color (plus he reminds me of a character from a different game).
Zucker - I wasn't sure about having one of the octopus villagers but then I saw him in my tent and couldn't resist to have him move in. I think he is pretty cute, especially when he makes this watery eyes. <3
Muffy/Willow - I plan to have them both. I find the sheep villagers cute and Willow was one of the villagers I just knew that I must have her and Muffy is one of the only uchi's I like and her design is really nice.
Marshal (obtained)- I heard about how great he was throughout the forum, visited some towns, and fell in love with him! Zucker- Any food related villager is a favorite of mine. Freya- I love pastel colors. I also like that she seems to be all mature and girly, but she's actually got a bit of a rock 'n roll theme to her house. Sprinkle- Again with the food. c': Bam- I've heard lots of good things about him, and I personally love the deer villagers. Hamphrey- I fell in love with him from watching LinandKo's videos online. Merengue- Food, food, food! And I love the fact that she was created to look like a cake. Flurry (obtained)- She's really cute-looking, and, again, her sweetness reminds me of my guinea pig. ♥ Agnes- I had her in my first New Leaf town, and fell in love with her. Her house is really neat too! Chadder- Who doesn't think a cheese mouse is cute?
I don't have any dreamies, but there are villagers I have purposely sought out. Most of these were because I had them in a previous game (Chief, Static, Walker). Other villagers I take in because I think they're cute, but everyone leaves my town eventually.
After deciding that I wanted to do a bird town, I checked the villager list and narrowed down to the personality types to have at least each in my town. Then I looked out for villagers that appealed to me by their appearances.
Personally...I tend to go for looks as well.
I also decide based on the personality that they hold. I would go through a list of villagers from each personality and pick the ones I found visually appealing. It's mostly because I find the personality types to be exactly the same no matter the species, so I might as well get pretty villagers.
My Dreamies some obtained all fitting in with my in progress cute/pretty town theme:
Merengue- So cute love her eyes and has a strawberry horn.
Tia: So cute, love her teapot head.
Stitches: adorable stitched bear too cute^_^
Chief: Reminds me of an anime character I love and his eyes are awesome, love this addition.
Rosie: Adorable to the max xD
Bam: Blue is my fave color, I love deer. Perfect match.
Whitney: Love wolves and would love to add her to match with Chief=D
Diana: again would love this cutie for Bam xD
Mira: Sort of a dreamy, may let her go after initially getting her pic.