Since I've always gone for the reptilian/draconic starter, I'll be choosing Tsutaja, even though I'm disappointed that his look has no originality at all. He's neat, don't get me wrong, but damn he looks way too much like Treecko. However much I like his design, original or not, every single grass starter has been a reptile...I wish they could've made the fire or water type reptilian instead and broken that mold. Meh.
I have mixed feelings about Pokabu as well. His expression in the official art is...annoying, but his sprite looks absolutely adorable. At first I wasn't too keen on the pig idea, but now that I see what it really looks like, it was fairly well done. I think the evolution should be especially interesting.
Mijumaru is very, very cute even though he seems too similar to Piplup/Pachirisu. He rather confuses me, though - is he a polar bear, an otter, or a mix of both? It's likely he'll have a dual ice type, since he closely resembles a snowman too.
Overall, I have very mixed feelings on all three of them. I think they're a step up from Gen 4, which was awful imo, but they're definitely not perfect either. Still, the evolutions are all that matter to me; as long as they look cool, I'm satisfied.