Best: having your child, them smiling, laughing, hugging, kissing you. Seeing them do things for the first time. The crazy love like nothing else.
Worst: lack of sleep, not being able to do what you want at the drop pf a hat (especially in the winter when you have to start getting ready 1/2 hour before having to leave), lack of sleep, depending on your age maybe losing friends, oh did I mention lack of sleep?