I haven't changed them all yet, but my mayor will have Kiddie Zen Castle, second character will have Mermaid Castle, and third will have Sweets Mansion. Fourth character will have some kind of Modern house, although that won't be for a long time.
Hmmm, I like the regular mansion the best, the zen one being a close second. My mayors house is a tropical grass hut mansion and it goes well with the rest of my town ^_^
I voted castle, cuz that's my mayor's house. My other 3 characters are the regular style.
I think the cutest though is the startup house. Once you start expanding and remodeling it, it's not too cute. But the first couple of days it's adorable. Makes it look like a little smurf village. I think it would be cute in a natural town to have 4 tiny 1 room houses.
I have the castle, with Fairytale exterior. My second character I use for storage has a home right next to mine, so when I finish upgrading that house I'm going to give it the Zen model.