First lets define what each division is and it's requirements.
Competitive - There are no gender requirements. All skill levels welcome, typically for experienced players.
Social - There is a requirement of at least 2 of each gender on the court per team. All skill levels welcome, best for new players.
Many people sign up for both, so skill level will vary throughout. Social is the best division to sign up for if you are new. Competitive division is best for those that want to get in on the action.