My experience of online dating sites was awful, but I'll give my honest opinion on the ones I tried.
Match: A pay site. Due to that not many time wasters, or people creating false accounts. The downside is the site is set-up to trick the user into thinking there are more people registered than there actually are. You can create an account but never pay and thus you can not message or respond to messages, but you have no vision of who has paid and who hasn't. You also can't tell who may have let their account lapse and never deleted their account. This gives you a false impression on the amount of active users in the area.
Plenty of Fish: Free site and comes will all the troubles of being free. If you are a woman and reasonably attractive expect your inbox to be bombarded with messages and have to wade through the dross of sex messages and guys just writing "hi" to find those actually serious and making an effort.
If you are male expect to send numerous messages and get no response, even when you have spent time reading profiles and writing a message based on what the lady has written. That is if she can muster more than "I don't know what to write, message me lol" for her profile. The mantra for PoF is 'no reply is a reply'. The place has many users, but how many are seriously on there looking for a relationship is anyone's guess. Lot's of married/in relationship people looking for a one nighter among the singles actually looking.
Also the more popular people will often become serial daters, as they have a never ending line of new fish chasing them.
OKCupid: Was sparsely used in my area, but I believe it's popular in other regions. Another free site, but not as much of a meat market as Plenty of Fish. I can't really comment to much on it, as the user base was very low and thus I ended up hardly using it.
Guardian Soulmates: A pay site, but not many users in my area again. Those on it seem genuine enough, but like Match has the same pay site issue that you can't tell what users are fully paid up active members and who have created accounts but have never paid up.
My overall experience. In two years of online dating I couldn't tell you how many messages I ended up sending out. At least a few a week over two years, so a good number. I read each profile and tailored my message to the lady asking questions about interests we shared etc. I can tell you from that I had two dates, and only ever had replies from five different user. I got the online equivalent of radio silence when I asked if the other three would like to meet in person. Neither of the dates got past date one.
If you do it you need to be mentally strong to put up with the flaky nature of many users. Expect people to not respond. Expect someone you have been talking to just to suddenly stop. Expect that even though you've messaged each other that if you ask to meet up they may just disappear. Expect that many use old photos, lie about their age etc.
After two years I'd had enough. I had to admit I'm not what the single ladies in my area are looking for and have completely given up on meeting anyone now. Online dating works for some, but I must admit I found it a soul crushing experience.
