Ok, with all the talk about Litten and Popplio, I want to go past the 2 cents I gave earlier and give my 2 dimes.
On Colors: I decided to put all the starters onto one page in order to analyze their looks in comparison to past generation games, and it's very interesting. These starters are a huge departures from all of the ones that came before it. Grass starters have primarily been pale greens and yellows, with the small deviation of brown and more energetic greens for Chespin. Of course, we have never had something that is primarily tan, like Rowlet.
Similarly, fire starters tend to use oranges, yellows and tans, while sometimes using a dark color for emphasis like navy or black. They have never used a dark red before, so that alone brings Litten in as a huge departure, and the black being his main color just brings that further.
Others have also mentioned Popplio's difference from the water starters of old, which have been light blue, aqua, and white with minimal use of dark blue. We had something a bit brighter with Froakie, but Popplio takes the cake being dominated by dark blue and having no yellow or orange on his model, which every single other water starter has.
Litten: I didn't think this Pokemon would be getting the hate it has gotten. Not that it's getting a ton of hate, but the reason people dislike it surprises me. It's simple, and that's the reason people don't like it?
When I first saw Litten, he rose to be one of my favorite starters, taking place right below Rowlet. I honestly love when starter designs are more simple. It leaves room for a lot of expansion in the future with it's evolution and makes it feel more natural as a pokemon. I don't get why people want him to be so much more complicated.
I also love the color choice. Having black as the primary color looks really good, especially with the dark reds to emphasize things. He looks different than all fire starters before him, but it really works and in my opinion looks very cool.
Popplio: Now after defending a somewhat disliked but mostly disliked pokemon, I am going to give the detailed reasons I personally dislike a mostly disliked pokemon to explain to others.
The primary color of dark blue is a huge offset that just makes him look strange from the beginning. The white part looks like an ice cream cone stuck to his face and doesn't seem like a natural part of him. All other water starters have had legs, where he really doesn't, having a flipper at the back which feels kind of strange. The ears on it's very round head also just look very strange, although it's hard to explain why. Lastly, I tend to prefer the simpler starters (like Litten) and being so defined as a "circus animal" with the neck frill and stuff doesn't appeal to me as much.
Overall, I like Popplio's attitude, artwork, and think he could be cool, but he doesn't have any initial pull to me.
And on other starter stuff: I will not be waiting to see what they end up as to decide, mainly because that's one of the surprises I like to keep for the game, finding out my what my starter will become. I'm surprised to see so many people decide based off the final evolution, as I view picking a starter as someone who I'll grow to like during the adventure no matter what they become. If I like them at the beginning, I'll like them at the end. When I played Red originally, I picked a starter who I liked not because they'd be Charizard or Blastoise, but because they spoke to me from the beginning. So, Rowlet will be coming with me the whole way through.