I liked them both. If you're into family sims, there are some new interactions. Some of my favorites are between kids and toddlers. There's an awesome kid/toddler hug and watching kids play peek-a-boo with the toddlers is priceless. There's also sending kids to private school, after school activities, imaginary friends.
Late Night has a lot going for it as well. Vampires and new dance moves (club dancing). Celebrities. Though I have to use a mod to control both vampires and celebrities in my games, they spread like a virus. It's no fun when every single townie is a celebrity.
You'll get a lot of gameplay out of either expansion, really, so it depends on what you prefer.