New leaf and ACWW are tied for me..i got into playing when i got ACWW so it has the nostalgic value for me but new leaf really made me fall in love with the series again while city folk killed it for me and i never have played the GC version because i got the gamecube very late in it's lifespan
New Leaf was built from the ground up, mixing in some of the best aspects from the prior games, so it wins out just because of how well they developed it. Plus, like its handheld predecessor, the series is perfect for on the go, because if you play it in real time, you can take it everywhere, never missing an event again because you weren't at home to make it in time- I ran into that a LOT in 2002/2003, and refusing to adjust the clock, I was SOL. After 2005, never again did I ever miss a time based event. Of course, that demoted Animal Crossing and City Folk to lower than Wild World and New Leaf. Because of the Virtual Console though, we're never going to see NES game return to the series. If it weren't based in real time, maybe the handheld iterations wouldn't be so high, but it IS based in real time, and since my virtual town runs in the same time as my real life, I'm voting both handheld versions as my favorite with New Leaf edging out Wild World.
Gamecube because for me, it's been the most wholesome and had some unique qualities to it that none of the newer iterations compete against. The small details of the GameCube version such as the personalities of villagers, the coversations, the simplicity and homey-ness of the whole town, and the large size with a max of 15 villagers per town really made it feel like everything was there to create the memories you needed.
Maybe I'm just nostalgic, but I also won't disagree that new leaf is the new second best. (All it needs is a similar sized town layout and multilayer towns and some better/more personable dialogue from villagers and everything would be perfect. It's a shame that in new leaf, the towns are flat again. But hey