Definitely New Leaf, as far as I'm concerned. WW and CF bored me, the original was the only one that held my attention for long. I'm sure the one coming out on the Wii-U will be great after what they've done with NL, but I don't want to buy a whole new console just for one game, y'know? =_= So yeah, I'm sticking with NL for quite a while.
New Leaf, but Wild World villager personalities and dialogues are way better. I also enjoy WW soundtrack more. Hopefully they can improve the dialogues and town size in the next AC :B