I woulda thought that eHarmony would have been the best bet since they charge a lot of money, have a intensive interview process and their branding is defined on finding potential marriage partners. I tried match about 8 years ago, and it was meh, but this was also before the dating site boom so maybe it may or may not be better now.
PlentyofFish looks and feels kinda trashy, it’s not well designed and the community is kinda lowest common denominator looking from a female perspective. I’ve seen messages that my female friends have gotten from guys, one thinking that simply because he has a 13” dick makes him totally worth a date. (And his “proof” was a pic lifted off a porn site).
I’ve had my best success and met my current girlfriend on OkCupid. Their matching system isn’t perfect, but they have a large pool of users to draw from, and many of them are quite literate, the ones that aren’t high quality are easy to spot. There’s still a fair bit of people looking for action, but OkCupid’s system does account for those looking for casual sex only, and filters out (or in) those kind of people in your search results if you tell OKC that’s your goal. It’s very much free, and the only benefits to their paid model is that you get your face as a priority listing in results and you can post more, and dirty pictures (free users can only upload 5–6 pics and must be non-adult)
Whatever system you use, it does require patience. The common expectation on using one of these sites to try to widen your net is it will get you great results fast, and that is not the case at all. Sometimes some people luck out, others will spend some time. I spent nearly two years on OKC before I found my current s/o, and had to endure a lot of dead ends, bad dates, good dates that never called back, crazy women, and people who honestly had no clue what they were doing to get there. Try not to focus on the endgame, it will drive you insane and depress you cause you have no idea how long/short it will be before you find your place. Just enjoy your time (however short) with the people you do meet and it won’t feel wasted.