I can't pick a single favorite sim, but my favorite household to play at present is my hippie commune, the Dinglewood Ashram.

Currently three inhabitants, brother and sister Shaggy and Sunshine Rogers, and Shaggy's girlfriend, ex-townie Mary Allen. He's romance, the girls are respectively popularity and knowledge.

They're all sloppy, nice, Grilled Cheese-secondary nature-lovers, and I let 'em have free range most of the time. (I fix routing problems, etc.) They make money by farming, both from legitimate organic farming, and from, uh, "other" farming (money trees, in a stand-in role). Regular jobs are for the Man, man. The place is built and decorated with the more bizarre and useless items from the windows, doors, and decorative catalogs.

Eventually they will open a business; possibly a restaurant, as there'd be enough adults, and Mary has both 10 body points (which I hear is good for waiters), and 4-5 cooking points.

The place is full of groovy vibes.

(Yes, if they get a dog, it will be a great dane and I will name him Scooby-Doo.)

My favourite sim at the moment is Sally Riley from Belladonna Cove. She's just grown up to a teen and I gave her the knowledge aspiration, which seemed the most fitting as every 5 minutes she's banging out a tune on the piano or painting. I gave her a cute little light brown bob, some freckles and she just looks absolutely freaking adorable!
That said, her father Timothy is an absolute pain in the rear. Everything he does just seems to irritate me, and he generally just wastes his time sleeping or whinging about something. Or causing fires.