Do you go big and create a pack of Velociraptors? They'll definitely excite potential visitors, but you'd better make a large enough enclosure for them. And maybe hire some (read: a lot of) security. Or they WILL break out and start eating your visitors, and we all know how that ends. You could play it safe and grow a bunch of herbivores, but then you aren't going to have the most exciting park in the world (sad face). So maybe buy a roller coaster or two to attract visitors to your park the good old-fashioned way?