My favorite has always been Daisy! Shes just so adorable and down to earth, and she gave me the best nickname I've gotten in an AC game. :3 I do hope she returns in 3DS and I can get her as a villager.
I remember I liked Static and Chow on the Gamecube. Once I had Aurora and she was nice too. So they are 3 of my favorite neighbors I have had. I like most of the neighbors if not all I have had, those three are just probably the most memorable. Right now I have Chester the panda bear. I would have liked it if he was sweeter or sweeter and a girl.
My favourites/closest friends from 2006-2012: Mitzi, Poncho, Bob, Tabby, Lily, Drake, Blaire, Aurora, Dotty, Roald, Sally, Rod, Samson, Yuka, Vesta, Stitches... I have so many ^_^