I'm gonna do that thing I always do where I find someone with a 3ds and get them to trade with me until I'm able to get all 3 starters on one save file.
If I had to choose though it'd probably be Rowlet. It's cute and I'll be able to make fun of Fire Emblem archers with the final evolution. "You betrayed your family and Hoshido!" "I am betrayal!" "Filthy sub-humans!" etc.