Tough pick between Wild World and New Leaf for me! I would love to play the OG AC as well but I don't have a Gamecube so I doubt that will be happening any time soon. I have played every game from Wild World onwards though.
Wild World was my first Animal Crossing game and boy did I love it! I remember working a shift at Nook's, making star constellations, having long and engaging conversations with my villagers, enjoying the silly little events (Acorn festival was one of my favourites), going to each villager house for the flea market, unlocking the shop upgrades, the best looking house exteriors in the series (IMO) etc- the list goes on. It was my favourite game as a kid on my DSI. CF was very similar, I only played it on a friends console semi-regularly but I found that it did not hold the same charm. The wii remotes were really frustrating with it and it wasn't worth a lot of time given how similar it was to WW.
Then came New Leaf, the villagers were a little less interesting in dialogue but the new features were extremely exciting! I loved being a mayor of my own town and using ordinances, working hard to unlock PWP's, working shifts at Brewster's, unlocking Mainstreet upgrades, spending countless hours playing at Tortimers island + mini-games with friends, playing hide n seek, swimming, the expanded catalogue plus new villagers etc. It was the best game for playing with friends both local and online imo and had a great balance of things- it wasn't purely designed for those who loved customisation like NH is, but was also designed to enjoy the relaxing, day-to-day relational aspect of ac as well. There was so much more to do in comparison to Wild World and I loved every minute of it. I would argue that New Leaf has just as many features and detail, if not more than New Horizons. As someone mentioned above, thought was put into everything- even tree stumps and appointments for villager visits!
I still play both New leaf and Wild World to this day, they are great games with a lot to offer. Wild World has a charm that I haven't found in Animal Crossing since and is very relaxing, New Leaf is just loads of fun and I have grown very attached to my town over the years.
As for New Horizons, I like it, I enjoy it and I think that some of the new features are just fantastic- BUT, I wish that it wasn't solely focused on customisation, that has never been my thing. If I wanted a game full of customisation I would be playing Minecraft or something of that description, I feel a lot of pressure to mark my style all over my island as that is its purpose- to look good. Without any chores for villagers, lacking dialogue, items, mini-games, expansive shops with working options etc... there just isn't much to do in the way of relaxing, daily activity. I don't get the same charm from it I do from the older games. I still play it but I take big breaks. I play maybe 5-10 sessions over the course of a week (all maybe an hour each) and then stop playing for a couple of months. However, I have much less time on my hands these days than I did when WW and NL were released so perhaps when I have more time next year I might properly get into the game and love it the way that others do. For now, my vote goes to New Leaf for being a wonderful balance of content and charm, I love this game to death.
I haven't addressed PC or HHD as I do not consider them part of the main series but I will say this- I still enjoy both and think that they are great for what they are despite the criticism. Amiibo Festival though? Nope.
. Decorating outside is great but i am out of ideas; I have run out of inspiration with the current selection of furniture. Nl had such wonderful furniture and clothing and we could customize items with clothing (i think with qr code designs as well). But we couldn’t decorate outside. But we had the museum extra rooms to decorate which was fun. I definitely enjoying interacting with my villagers more in NL. I love being able to buy items from them in their house and them visiting my house and commenting on my decorations.
