Superman's hugs are warm, the perfect amount of tightness, and not too long but not too short. The hug of a close friend you haven't seen in a long time.
Wonder Woman's hugs are longer and gentler, more comforting and soothing, and there may be a smooch at the end. The hug of a mother.
Batman's hugs are extremely rare, and you'd likely only get one if you are one of his loved ones. They are long, very tight, and almost desperate. The hug of someone who doesn't want to lose you.