I've had luck with both paid and unpaid sites. Currently dating someone I met on OkC and that is going well, so I'm biased right now
But, as someone who had over 40 dates in 3 and 1/2 years, perhaps I'm not the kind of expert you want to hear from :) All sites have their positive points and negative points. Difficult people are on every site...
Profile advice: Have several recent pictures on your profile. At least one should be a full body type picture. Show your best self, smiling, being happy, doing something that you like to do, a vacation shot--something that can get a conversation going. Men are visual. They will look at a profile picture and make a judgment, so portray yourself in the best way possible. Have a friend take some good photos, or although I never did this, consider getting professional pictures taken--telling the photographer "no glamor shots"!
Put positive statements in your profile, describe your interests, things that make you unique. I looked at other women's profiles before I formulated mine, as I wanted to stand out, not be a part of the crowd. Leave out the "absolutely no players please" type of statements. Leave out cliches like "I love to travel" and "I see the glass as half full"--men I've dated said they saw way too much of those statements, so that it lost its meaning. Saw an interesting TedTalk that mentioned it was good to be specific regarding what you were looking for rather than generic, so that is an idea too...
Men's profiles: If they have spent some time writing their profile, they are probably more interested in dating seriously. Less effort=less invested seems to be a correlation.
The best think I did was to read a book called "Dating Like a Grown Up" by Bobbi Palmer. I read it just 3 months ago and wish I had seen it early on...changed the whole dating experience for me to a much more positive and centered thing. Helped me focus on what I wanted, not on what I thought I wanted. I highly recommend it.
Good luck dipping your toes in the dating pool!