Not only do you have the best chance of seeing a Sri Lankan leopard, but you also have a very high chance of seeing elephants. We went during a period of time that Yala national park was experiencing a mini-drought. This meant that the elephants were further inside the park around the permanent lakes and not need the main roads. Even then, we still managed to spot a lone male grazing in amongst the trees. If you go to Yala when there are not experiencing a drought then you will certainly see herds of elephants roaming around the park in plain sight.