The following comes from IGN in regard to Oshawott being the perfect starter Pokémon for Batman/Bruce Wayne:
Not only is Batman the World’s Greatest Detective, he’s also one of the best tacticians out there. How else could one man with absolutely zero super powers manage to defeat super villain after super villain alongside the likes of Supes, the Flash, Wonder Woman, and Green Lantern? This knack for strategizing should make him a pretty brilliant Pokemon master (after all, if anyone can figure out and master EVs and IVs, it’s him). Still, good ole Bruce isn’t exactly great with the warm and fuzzy stuff, which might make it a bit difficult for him to develop a relationship of trust with his Oshawott. It also doesn’t help that he’d probably despise that sweet, little otter and his big, goofy smile. Just saying.
Source: Former IGN editor Audrey Drake