Rowlet is definitely my favorite of the three. I really like birds, especially owls, and I'm also fond of the Grass-type as of late. It's really cute and I'm looking forward to finding out what its evolutions look like and what its shiny colors will be. As of this moment, it's one of my favorite starters from all of the generations.
Litten is second. It looks good and its coloration is nice, but it just doesn't have enough to put it over Rowlet.
Pipplio is underwhelming, especially because we already have so many seals. I won't judge it too harshly until I see its evolutions, because I think it can potentially go somewhere interesting once it evolves.
I don't know why but I have had bad experiences with Chikorita holy craaaap the first gym in johto >.< so I don't especially like grass starters, no matter how cute or cuddly they are. I don't really like the water starter because Oshawott exists and so does Dewgong. The LITten 420 *smoke signals* *smoke signs* *smoke* *house burns down* just seems so cute and powerful. I absolutely love cats and foxes and anything with those type of ears, so Litten is definitely my favorite. I hope the evolution of Litten is as good as I hope, or Rowlett I'm comin' fo' ya.
I always end up with water pokemons, so i will go with Popplio. I also want to specialize on Bulky water pok?mons or sweepers. But I think Popplio will end up countering Rowlet if Popplio's evolution ends up Water/Ice like Dewgong and Walrein.
But ignoring the fact on who counters who, I like all three starters and none should be appreciated any less.
I can't decide so far but I'm interested in getting Litten the most because it's a cat. They all look okay to me, but I'll just wait if they will announce the starters' evolutions soon.