I've gone through a lot of these over the past couple of years. The big mainstream platforms have the numbers but also the most garbage to sort through — bots, inactive accounts, profiles that haven't been touched in years. The niche platforms can actually be better if you're in a reasonably populated area and willing to do a little digging.
The names that keep coming up in threads like this one: Tinder, Bumble, Hinge, OkCupid, and Facebook Dating on the general side. For more intent-specific platforms the landscape shifts. Worth comparing a few before committing to anything.
Someone in a thread similar to this one pointed me toward Flamedate and so far I've been reasonably satisfied. The free features are actually functional, which puts it above most of the competition.