I felt that both have a lot of potential, and I believe both were decent rivals, I just felt that they needed to be executed little more.
The fact that you face them regularly is what I liked most about them, it makes them a part of the story and not an afterthought, that's also what I liked about barry and silver, they were a relevant part of your journey.
I never liked gary because not only is he incredibly shallow but you only see him a few times, and the 3rd gen rivals really could have went better, brandon and may don't even try and even give up later, and wally really needs to have encountered the player more throught the story, it would have been nice to he how he grows along with the story.
Cheren and bianca seem to lose out in favor to most fans because they aren't anghsty like silver or strong like gary, but that may just be me.