Predictable answers all over the place. :( Froakie has the most interesting character design, I think. The grass starter is kind of by the numbers, and the fire fox, well, we already have one of those. I hope it's actually a wolf, because I really don't see why they went there again. Vulpix is still the cuter of the two.
The thing is, the grass and fire starters look like the model Pokemon design, which is why I would expect people to pick them. Froakie has a more cartoon design which is probably more appealing to those who aren't used to seeing the Pokemon house style all the time. We'll see how that plays out, though. I remember when people thought Oshawatt (or however that's spelt) looked bizarre.