Most Helpful Guy
It's the best one, IMHO. I found the love of my life there. I tried Zoosk and POF, too. I heard bad things about Match and eHarmony, so I didn't go there.
They have a system of questions that works better than any other site. When you sign up, they ask you to answer at least 50 questions that reveal what you are like. There are over 2000 questions. Then, when you look at someone's profile, you can see how they answered every question that both of you answered. Now, here's the killer feature: you can also see all the questions that they answered but you haven't, but you can't see their answer until you answer it, too. A natural way to improve your profile at the same time you find out more about this person.