I think it's important for teens to enjoy reading because adolescence is the time when people really begin to form their values and worldview independent of their parents and family. A lot of times, this is pretty heavily influenced by their friend group, which tends to think in similar ways and have similar biases. If teens are reading during that time, though, they're getting lots of different perspectives that can either confirm or challenge the values they're forming. Reading can help teens critically consider and adjust their worldview in a way that friends and peers often won't, which I believe is really valuable.
It's really hard to pick an all-time favorite book, but I'd probably have to choose A Thousand Splendid Suns by Khaled Hosseini, which is about an abusive husband and his two wives during the Taliban's rise to power in Afghanistan. It's not one of those pageturners where almost every chapter ends on a cliffhanger, but I still finished it in three days because I was so captivated. The writing is beautiful and haunting, and it gave me a perspective on and compassion for abuse and the problems in the middle east that I never could have gotten from statistics or news coverage. If you're looking for a feel-good novel, I can't say I'd recommend the novel, but I think everyone could benefit from reading it.