Here's what I thought of the starters individually...
Chespin - looks okay I guess, could be a chipmunk with a chestnut hat or something? I don't love or hate it's design, I'm just curious to see what the rest of it's evolutions look like and what the hat thing could turn into. If the attacks it used were hints at it's final typing my guess would be Grass/Dark. Seemed like it first used Solarbeam and then Night Slash second, which is super effective against Golurk.
Fennekin - I like Fennekin a lot because I like fire types in general, but I found it to be a little repetitive of Vulpix. But it looks cool enough in it's first stage and I want to see where this fire fox design goes. Hopefully it doesn't look like any of the other fox pokemon. For the final typing I would guess Fire/Psychic, because it looked like it used Flamethrower and then Psybeam or Extrasensory.
Froakie - my favorite so far and the most interesting to me, I can't see why everyone is hating on it. I actually like it's design and it looked good in battle. Seemed like it had good speed, a trait I value. For the final typing I have two guesses: Water/Fighting and Water/Flying. I said fighting because it looked like a physical attacker when it was in battle judging by the second attack. As I thought of more possibilities, I came up with Water/Flying because of Froakie's design. It has what looks like a cape around it's neck or something that looks like a cloud. Maybe that could turn into a parachute or something? I looked it up and read about something called the Malabar Gliding Frog. It's a frog that jumps from high areas and glides to get where it needs to go, so I could see where a Flying type inspiration could come from. I couldn't figure out what the second attack was, but I thought it could possibly be Acrobatics, a flying type move. I'm hoping it does develop into a Water/Flying type, because there is already a fighting frog (Poliwrath), a poison frog (Toxicroak), and a ground frog (Seismitoad) so I think a flying frog would be cool.
Usually I go with the fire starter, but I would have to see their complete evolutions to really make a decision. Right now Froakie appeals the most to me but they all have potential. Can't wait to see their full evolutions though. I'm just hoping for some new type combos this time around, and Fennekin better not become a Fire/Fighting type somehow.
Chespin I think will stay Grass type all the way through. At least that's what the design looks like.
I think Fennekin will evolve into a psycho-fox or something, and be Fire/Psychic. That could be an interesting type.
Also, as for Froakie, I would go for a Water/Poison might happen. Some toads are poisonous. Or perhaps the Water/Fighting combonation. Although I think they will be looking for unique type combo's in Gen VI.