Which Rival's story do you like the best and why?
Definitely Silver. Nothing much was ever explained about him, especially not through the original games, and we just went on thinking he was some idiot constantly getting in our way, and for some reason he really hated Team Rocket. Then we learn that Giovanni is actually his father, which from there we can just guess why he's such a bitter person, and it's easier to understand why he turned out that way. Though there isn't much to his backstory, it was easily the best of any rival that has ever been in any of the games, especially as most didn't even have one.