Candids are my absolute favorite. I had disposable cameras at every table at my wedding, so everyone could take candid shots of whatever they wanted. I got many different perspectives of our celebration!
My husband's favorite photos of our children are candids that I took. The problem, in my opinion, with formal portraits is that they're "perfect" and have no personality. My best friend had portraits taken of her youngest son when he was about 4. In one of the photos, one strap of his overalls slipped down. The photographer almost didn't include that picture when he showed her the proofs because it wasn't perfect, but she absolutely LOVED it and that was the one she bought - because it showed his personality, the look on his face when the strap fell. That strap was ALWAYS falling down, and that photo captured him perfectly and made her laugh.