I can vouch for Bastien's route! I just played Leopold, Guillaume, and Bastien in that order...
Leopold was amazing and everything I wanted
Guillaume I really disliked for 90 percent of his route and it was painful to get through with everyone else being mean/unfriendly
Bastien was sad but way more believable as an actual romance as well. He really starts resolving and working on difficulties he has while communicating with you in a very sweet way. And not in the end of the route like Guillaume but about halfway through. He is no where near as mean and annoying as Guillaume and your brother is with you for support and hilarity.
Def play Bastien's route <3