Ooooh good question! I think it would have to be exotic for me as that's always the first set I focus on getting in a new game, and default one I use. I love the customised version especially!
I really love the princess set because I think it's a different play on princess since it's not pink and super frilly. I also reallyyyy like the rococo set, I really like the art style and I think the set does it justice I'd love to have a rococo room in real life <3
Oh man, that's really hard for me to answer! A lot of them look great depending on how they're arranged.
My favourite has to be flower set you get from Weeding Day. I love flowers (I even do floral design irl), so an entire furniture set based on them makes me quite happy!
I also love the mermaid series, but I never use it in its entirety since it's overwhelmingly pastel. It just doesn't fit the overall feel of my home. I love seeing it used in other towns, though!
Mine is the Alpine Series because it's different with a change of clothing or a QR code.
I've seen Alpine furniture using a Gracie clothing and it was really nice. One year I sent all my villagers Alpine Sofa with the Ball Tee Number. Villager One received the One Ball Tee.
Someone posted that they redo the Alpine Panel with their flag on it. They send it to the new villager with a welcome to the town letter. Nice idea.
hmm I really like the alpine & cabin set! but however, unorderable it would have to be the weeding day set, fish set, or bug set. I'm so in love with them, lol.
Probably the mermaid set...or the sloppy set. Both really different to each other but the mermaid set is just so pretty with the floor and wall too. Plus I can use my fish furniture with it and it looks great. The sloppy set just looks like a great room to relax in when all the furniture is in place. Just chilled and relaxed