There's lots of discussion of this topic in these forums... you might want to search.
But the short version is that depending on where you are, each app can have a very different audience. One is not inherently better than the other, and one may be better in some locations than another. In my town, Scruff is very bear-centric, Grindr is very twinky, Jack'd skews very Asian. When I go to other cities, Grindr can be much more mixed, Scruff can be very otter and rugged muscle guys with the bears being on Growlr, and Jack'd can skew very heavily African American. The only way you will know is to check them out for a while and see how they shake out in your area.
Also... surprise! Six months later, the population will have changed and might be completely different.
For this reason, many people are on multiple apps... precisely because you never know where you're going to meet someone to your liking. Some people are lazy and don't want to be on multiple apps... that's fine, but they shouldn't complain that they're not meeting a variety of people.
And all the apps can be for both hooking up and for meeting people for relationships. I've hooked up from "dating" apps like Tinder and OKCupid, and I've had multi-year relationships with people met via "hookup" apps. I disagree with anyone who says any app is "hookup" or "dating" oriented, they're all for anything -- which leads to my final point...
Finally: you will get out of it, what you put into it. Communicate your interests clearly and you'll be more likely to find someone interested in that. Looking to date? Say it. Looking to fuck around? Say it. Looking to fuck until you accidentally stumble into a relationship? You and everybody else!
PS: Please have a fucking picture fer chrissake, or send one with your first message. If you won't show your face, most people will assume you're some kind of closeted psychopath.