So far there have been 13 rivals and i want to see which ones you like best. You can choose from Blue, Silver, Brendan/May, Wally, Lucas/Dawn, Barry, Cheren, Bianca, Hugh, Calem/Serena, Trever, Tierno, and Shauna.
Haven't played Sun or Moon (UK here), so for me, its got to be Silver, because he went through character development and ended up bonding with his pokemon.
However, I wouldn't class Lucas/Dawn as rivals as you can't battle them, they teach you how to catch pokemon and also battle alongside you, rather than battle you.
Bianca for me. An adorable girl who just wants to figure out who she wants to be in life, with a little help from her friends. She battles you at several points during the main story and can be rebattled infinitely during the post-game, which are good qualities for a rival.
I am also a big fan of Cheren, Hugh and Barry. They also had great personalities, great stories, they battled you many times during the story and could be rebattled infinitely as well. I just like Bianca better than them.
May/Brendan and Wally were also really good, just not quite the best. The X/Y group of friends were acceptable, it was an interesting concept but the execution could have been better. I haven't played S/M yet so no opinion on their rivals until I have met them in their games.
Blue and Silver are my least favorites. They are jerks with zero or very little character development, which I see a big failure when it comes to important characters. I didn't find their personalities or backstories (or the lack thereof) very interesting either.
Even so, it is still far too little and can't be compared to that of Bianca, Cheren, Hugh, Barry and Wally, not to mention it happens way too late in the game compared to the others. I just don't find him or his small bit of character development very interesting.Silver was a jerk, who stole his starter, and literally used it and his other pokemon as tools, through is constant loses to you, he came to realise that his way as a trainer was not working for him to be the best, and began to see his pokemon as creatures with thoughts and feelings themselves, this is shown through the evolution of his Golbat, which was Golbat for a long time, until it finally evolved through happiness and friendship. Plus he's the son of Giovanni.......
He's got tons of development.
Even so, it is still far too little and can't be compared to that of Bianca, Cheren, Hugh, Barry and Wally, not to mention it happens way too late in the game compared to the others. I just don't find him or his small bit of character development very interesting.
Blue, he was a total jerk and I wanted to see him lose more than the others. Plus I miss being able to give the rivals horrible nicknames, it gave Blue and Silver a good reason to be defensive and rude all the time. Honestly besides Barry and Hugh they've all been forgettable since Silver anyway. And neither seemed very formidable as people.