Choosing between New Leaf and New Horizons is kind of tricky. They both have their good sides and bad sides, and it can be tough to decide which one's better.
New Horizons definitely wins when it comes to looks and QOL. It's got the best graphics out of all the Animal Crossing games, and it brings in cool stuff like moving buildings and houses, dressing room at the clothing shop, a wardrobe for your clothes, storage, wands, Happy Home Paradise, terraforming, and the ability to put furniture outside. If New Leaf had the same graphics and these features from New Horizons, and be played in 1080p, it'd be a slam dunk.
However, when it comes to the town itself, and everything within, New Leaf takes the trophy. In New Horizons, you're kind of stranded on a deserted island with ocean at every corner and edge. It really feels depressing and isolated from the world. In contrast, New Leaf's town is just stop along a train route. This stop has its own little shopping strip mall that grows and gets better as your town does. Here you can bump into random villagers there, even ones who used to live in your town. Overall, your town feels a lot more cozy, connected, and homier.
I could create a laundry list of comparisons, but we'd be here all day. In the end, the perfect Animal Crossing game would be a mix of New Leaf's great gameplay vibes mixed with New Horizons' awesome graphics and modern features. That'd be a game worth playing for sure.
Gameplay and town > New Leaf
Graphics and QOL > New Horizons