Went with Bianca. I don't like Cheren much either, but I hate her, she annoyed me to death. Neither of them would leave you alone, they just kept popping up, and it isn't even satisfying to beat them because they just act like it was just a fun match since you're bestest friends. No, I don't want to be friends, I don't care about your boring family drama, I'm clearly a better trainer than you, just give up, shut up and go away. And your hat is stupid.
/probably has competitiveness issues XD I hope next gen has a proper rival who isn't supposed to be the MC's friend, though.