Yala has more leopards. Wilpattu has fewer jeeps. Which matters more depends on what you came for.
Sri Lanka is the best place in the world to see a wild leopard, and that is not marketing. The subspecies here has no competing large predator, so the cats behave differently: they are active in daylight, they use the roads, and they are far less shy than leopards anywhere in Africa or India.
Yala
Block One has the highest recorded density of leopards on earth. It also has, at peak season, a queue of jeeps at the gate and a radio network that means twenty vehicles converge the moment anything is spotted. You will very likely see a leopard. You may see it over someone else’s roof rack.
Wilpattu
Larger, older, far less visited, and structured around natural lakes rather than scrub. Sightings take longer and are less certain. When they happen you are usually alone, which is a completely different experience of the same animal. The drive up is longer, and worth it.
What we recommend
Both, if the days allow. Yala first, so the pressure of seeing one at all is off, then Wilpattu for the version you will remember. If you only have time for one and you care more about the encounter than the photograph, go to Wilpattu.