My first Starter for Alola is most likely going to be Popplio this time around.
Rowlet and Litten are just as good, though.
Rowlet's the first dual-typed starter since Bulbasaur. That's one way to make a strong nod to Gen 1. I reckon it will have balanced stats as it evolves. I think it would evolve into a wise old owl.
Litten, I speculate, would evolve into a fierce Fire/Dark Type Fragile Speedster, if not, a Glass Cannon. I reckon it would evolve into either a panther or tiger. The comparisons made to Ryuko from Kill la Kill are quite funny.
And finally, Popplio is probably going to be a Lightning Bruiser, given it's current bio as of now. I think it will become Water/Fighting, just to complete a circus-themed motive the new Starters seem to be showing.