While Sigiriya Rock is rich in history and has some pretty dramatic features such as the lion’s paw and the mirror wall, Pidurangala Rock has a much more natural feel, despite also housing a temple.
Pidurangala Rock is adjacent to Sigiriya Rock and is the best viewing spot of Sigiriya Rock as it is only slightly lower. Pidurangala is a popular spot for sunrise as you can enjoy 360-degree views of not only the valleys but also Sigiriya Rock.
There is no need to choose between the two. Many travelers wake up for the sunrise at Pidurangala and then head to sunset on top of Sigiriya Rock. This is exactly what I did and I highly recommend it.