NoStringsAttached has the superior design and pricing structure, but AshleyMadison.com is the top dating service for married men and women.
Media attention has boosted exposure, making the website a top online destination for cheating wives and husbands to initiate discreet affairs.
Built in privacy features help you avoid being busted by your husband or wife. You can choose not to openly display your photos, opt not to receive email notifications and credit card billing is discreet.
You don't have to sign up for a monthly subscription, which is a plus if you prefer not to be billed automatically. You simply buy credits whenever you want to actively communicate with members.
P.S. Don't join MarriedSecrets just because you receive emails telling you that someone has sent you a message. I received one such email when I set up my profile, but I know it was a phony message just to get me to upgrade right away.
I reviewed some other dating sites for married people, but I didn't mention them because most would be a waste of your time and money. You're better off using one of the services mentioned above.