I only use a few of them. I like clapping and joy and glee. The one dancing reaction--I think it's called "Feelin It"--is the only one of the newer ones I use pretty regularly.
I use the mischief one a lot. I also like the bewilderment one, since there is a funny sound that goes with it. Sniff has become another favorite of mine too (was not planning on using it a lot though lol ). And of course, sit. Great way to block @Pyoopi from causing mischief (sometimes) or @Mick
I like to use the apologetic reaction when I accidentally hit a villager with my net, especially if they had a thought bubble or had tried to ping me. Always gives me the feeling of stepping on a pet's paw, but it helps alleviate the guilt.
I use the laughter one a lot, because I like how happy it looks and it ends in the closed eyes smiling face, which is how I usually look in pictures irl. I also use confetti throwing a lot just cause it is fun and joyful. I use crying when I take my sad pictures of my villagers moving out. And sit…because i am still excited that one got added.
I like using reactions a lot, but mostly make use of just a few favorites.
I love reactions so I have way too many favorites. From the original 40, my absolute fave is Flourish, the little dance and stars is so nice. Other great ones are Joy, Delight, Bewilderment thanks to its amazing sound effect, Pride, Showmanship and Mischief.
The expanded reactions are... great. Like almost all of them. Haunt, Scare, Take a Picture, Sit Down, Excited, Ta-Da, Confetti, Viva and Feelin' It are so good and they set good interactions with the islanders.
joy is the reaction that i use most often and it just so happens to be one of my absolute favourites! i love how happy it makes my island rep look and the flowers are super pretty and a nice touch! i also love using the greetings, sit down eternally grateful to nintendo for this one, ta-da and confetti reactions as well! i tend to neglect the other reactions tbh but they’re honestly all great and super fun to use! ☺
My favourites are Mischief, Smirk and Laughter. I like using Smirk because of the varied villager reactions. Even Mischief gives me some mixed result, some even frown when I use it! Even though its not Halloween season, I also use Haunt and Scare on my villagers with one of my PCs thats ghost themed.
One of my favourite reactions to use is the sit reaction. It feels nice using it almost anywhere that's cozy feeling such as your house or a part of your island. Also, your villagers will smile at you if they see you sit down haha. The feelin' it reaction where you dance is my favourite as well.
I don’t really use reactions. Although, I like the angry one because it’s funny, but I try not to use it around other villagers. I don’t want to upset them.
I personally really enjoy the haunted reaction. Just how it looks, and how the other villagers react hahah. Otherwise, I also like sneezing and flourish (especially while sitting down)
I like using the blush emote a lot for whenever there's a moment of embarrassment or when flustered. I think it's kind of funny haha.
Smirk, mischief and sit are also favorites that I use frequently.
). And of course, sit. Great way to block 
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