The official Pokemon Sun and Moon website offers a couple of cool tidbits about Popplio. His swimming speed apparently can reach over 25 mph. Understandably being a sea lion, Popplio moves better in the water than on land, but this is true of most Water Pokemon. However, on land, it can perform tricks such as acrobatics using the elasticity of its Bubble balloons.
If I wasn't so excited about having a Fire Cat starter in Litten, Popplio probably would be my first choice for starter in Pokemon Sun and Moon. But considering that I have a commitment to using fire starters in every new Pokemon game the first time that I play, I'll have to discover the power of Popplio's evolution line later on. I really like Popplio.