I personally use the Vietnam style It's Called UFO there is another one very similar I have also called the HERO small fork gap but a great shooter.
You may want something with a very large fork gap or a black widow rock chucker. however just a natural fork with a daisy chain of rubber bands and a pouch will do the trick.
Make sure your allowed to have a slingshot as well some states and countries don't allow them and some do but with restrictions for example.
Here in South Australia, I can have one but it can't have an arm brace or any point to attach an arm brace
Long & short of it is anything with a wide fork gap, and it's always best to go tubes and a big pouch if you plan on slinging rocks.
As you get into the sport more, flatbands, and narrow fork gaps are the way to go for precision and distance. It's all subjective however so long as it feels good to shoot it's good for you. 80% of slingshot shooting is the shooter don't matter how good the catapult is.