Deirdre! I've had her in my first ever town and previous one and she is my favourite villager of this game.
If it were City Folk though, I'd have said Crackle. He has been living in my CF town for a long time and I was so sad when he moved out... I haven't ever had him in New Leaf (or even seen in-game, perhaps :O), so he's not really a favourite in this game anymore.
Of my current villagers, Lolly. Not because she's popular or anything, I just find her really sweet. :3
If I could choose any villager I'd have to chose Aurora. She was my closest friend in WW and I was so upset when we parted T.T. It'd be awesome to have her back again
But if I had to probably Skye because she is so adorable with the sky theme and she is my favourite colour. Oooh, I'll just end it here since I can go on forever about her XD