Well, you can actually convince them to stay! I have Wild world, and it's so much fun!! My favorite neighbors that I've had so far are Tangy the cat, Lily the frog (she's in my ds town) Kabuki the cat (again, living in my ds) and Alli the alligator!! (IN MY DS TOWN. XD) Mitzi, another cat is one of my faves as well as Wolfgang the wolf, but they moved away... :(
BUT IT'S FUN!!! I rented City folk before bought it!! I LOVE IT! xD