Owl with a bow tie works really well for me on cuteness. I dislike grass though, I usually prefer electric attacks to deal with water and water or fighting for rock. Still, grass flying might be an interesting typing combo. It's specifically ultra weak to ice (what isn't, really) but doesn't have the usual electrical or bug weaknesses of the separate types and offensively it covers 6 types with 1.25x super effective attacks, which could make for a versatile sweeper.
Depending on what the ultimates look like and their alternate typings, I can't make a final choice though. I usually lean away from water starts because every pokemon game has fishing and therefore a good variety of water types, whereas fire and grass tend to be harder to come by quality team members.