I have a few different reasons for choosing my villagers, but a vast majority of them fall under the "aesthetics" category.
To begin, here's my villager list: Bones, Fuchsia, Stitches, Sprinkle, Julian, Fang, Hamlet, Sylvana, Lily, and Judy
(Note: they were all my dreamies at one point, but I did eventually get them all, so that's why I'm posting this even though I do have them all)
When choosing my list, first and foremost, I wanted to make sure I had at least 1 of each personality type. While the reactions and DIYs are a part of that, I didn't even know about it until much later on. I just like having the different dialog options.
Bones is purely nostalgia. Wild World was my first ever animal crossing game, and Bones was one of my first 3 starters in that first town I ever made. Along with that, he's the first villager to give me a best friend portrait - so because of that, he's very special to me, and so of course I absolutely had to have him in my New Horizons island as well.
Sylvana is my birthday twin - while she's not a permanent resident, and will eventually become my rotating door villager spot, I did want to take her for a while, just to experience having my birthday twin on my island, just to have that plot filled so I can play around with designing my island.
Lily I chose specifically because she's a frog - I'm a sucker for small details, so the fact that the frogs don't wear rain gear in the rain I think is just an adorable thing to include in the game, and it makes me really happy. It's so unique, and I don't believe any other species has a little quirk like that, so I thought it'd make for a fun little thing to have on my island.
All of the remaining animals were basically chosen on aesthetics, for one reason or another.
I love Judy's pastel cotton candy look - she's just so stinkin' cute and makes me so happy to see her wandering around my island.
I'm a sucker for unicorns, so Julian was a must - his starry/zodiac themed house interior is definitely a bonus. So pretty!
Another thing I'm a sucker for? Winter aesthetics!! and because I needed a peppy, I just feel like Sprinkle was a pretty obvious choice for me. On top that, her design just... feels a lot less bland to me than a lot of the other penguins? (Aurora, Roald, and Wade, to name a couple off the top of my head - they're cute but they're too plain imo)
Fuchsia was a tough one - there's not really any other Sisterly's that match my aesthetics that well, and Fuchsia is the closest I got. Because of that, she's probably low man on the totem pole out of all the animals on my island? But I do still love her all the same.
Fang was another tough one - Because he's a cranky, there's of course not going to really be any "cute" themed crankies. So I tried to go with the next best thing, which was elegant? Was a pretty hard tie between him and Lobo though, because Lobo is SUPER cute. Fang won though purely because Lobo feels just a SMIDGE dark design wise for what I wanted on my island.
Finally, Stitches and Hamlet - they both kinda fall in the same theme of "kidcore", not quite sure what else to call it. They both have very child-like rooms, which is just adorable to me. There's something about the kiddie items in animal crossing that just make me so happy, and so I love the fact that these two villagers have it. Then of course there's the obvious, which is Stitches being a real life teddy bear. Adorable!
Additional note, Hamlet also vaguely reminds me of Hamtaro, which is one of the shows I watched nearly all the time when I was a wee one, so bonus points for that one.
And there you have it, all of my dreamies/islanders and their reasonings!!