I liked OkCupid because it let you see compatibility ratings based on questions. It was easy to weed out people who didn't try
Having said that OkCupid has gone downhill a bit since I used it to meet my spouse... shoot 4 years ago? Its still ok but now its swipey like the rest of them. Still way better than blind swipes but not as great. Still free though.
For absolutely most serious match is probably the way to go because nobody is paying money unless they are extremely serious
https://pbs.twimg.com/media/BdWiElvIQAAQpBt.jpg