Personally, I don't like taking portraits. No matter what, the expressions always come across as having some staged element to them. This may not apply to kids though. Their smiles usually feel more real to me. Maybe it's their innocence.
I've been a second shooter for a few weddings and usually the best photos are ones that I take during the in-between moments-- when the couple isn't worrying about the camera.
At home I prefer candid shots of normal everyday life. Maybe it's because when I look at the photos, it gives me a better sense of being "there". The smiles (or frowns) are 100% genuine.