I had to vote for Shin, just because he's so incredibly good (for a bow user at least) Fe6 hard mode bonuses are beyond comprehension, and it definitely shows with Shin. None of the other bowmen come close to him.
This was a hard choice. Not because I like them all, but because they all suck. But then I remembered Louise is a thing, and she comes with Pent, which puts her above the rest.