Why? I'm happily married now and haven't used a dating app in 5-plus years. The big thing that set OKC apart from other options when I was a user: It was free. But this was before a lot of advances in dating services. Tinder didn't launch until 2012, and by that time I was invested enough in using OKC that it never occurred to me to try a different app.
OkCupid is one of the most popular dating apps out there. You've probably heard of this one before. It boasts over 40 million people although we're not sure how many of those are daily active users. It uses a more traditional dating site method. It'll ask you a bunch of questions and try to find matches based on similar interests. It also has some more modern dating apps features, like swiping away profiles you want or don't want. It'll ask you to subscribe to a monthly payment plan to unlock all the good features. The app has some strict, ambiguous rules about some things and the app itself is occasionally slow and buggy. Otherwise, it's actually not half bad.
If you don't have the patience to weed out matches that are explicitly looking for a no strings attached hookup, a quick search on FriendFinder-X will probably make you pretty happy. You can search for potential matches using filters that range from proximity, sexual preferences and even cup size. Too lazy to search? The app has a list of compatible profiles sent to you for your consideration.