I agree with Old-Empresario. It depends on what (you) are after. There are thousands of different types of online dating sites as well as those with a specific niche. There are those focus on (common interests) race/nationality, religion, age, sexual orientation, political affiliation, those who have children, horseback riding, and the list goes on.
Finding someone who wants what you want is the key along with them being attracted to you! Never make assumptions.
Not all sites are equal. You have do your research!
However it's important to remember that (you) are responsible for (your choices) when it comes to selecting people to engage with whether it be online or offline. Odds are you'll overlook people who may have been ideal.
Online dating is just a (tool) for meeting people. It's not the (fork) that causes people to gain weight. It's (their) choices! Oftentimes when people have a negative experience they blame the whole industry instead of looking at (their) choices in the selection process.
I've had great online dating experiences but I also understand it's not (how) you meet but (whom) you meet that makes all the difference in the world.
Always use good commonsense when dealing with strangers both online and offline. Below are a couple resources you might wish to check out.
http://www.datingadvice.com/reviews (provides breakdowns of members)
http://lovealert911.com/ ( Has a free download: Avoid the Catfish!: How to date Online Successfully.)
Last but not least you may also want to check out Meetup.com This is not an online dating site. It is site that has 1000s of groups of people with various interest. The groups usually meet once or more per month. This is a great way to socialize with people you have things in common without the pressure of it being a date. One can gradually get to know people the way they would at work, in class, or other venue where people see each other regularly. They have just about every type of group you could imagine (wine tasting, book clubs, yoga, hiking, theatre goers, meditation, dancing, writers, singles clubs, and various sports enthusiast as well as professional network groups. Best wishes!