Mormons–the way they practice what they preach and the way they educate their members. My wife is LDS so I’ve had a good 3rd-person perspective on Mormonism for over a decade. Though I find their beliefs full of serious error, I do greatly admire their commitment to those beliefs, which honestly puts most of us Catholics to shame. Church-going Mormons dress appropriately for church, have reverent music in their worship (no matter where you go), and most importantly, know their faith a heck of a lot better than Catholics know Catholicism, which I believe is the single biggest reason why I keep running into ex-Catholics on their side.
Both adults and children go to Sunday school every Sunday, even through the summer. The bottom line is that the average Mormon is far more equipped to spread and defend their faith than we are. I wish we required (or at least highly encouraged) our adults to go to religious education every Sunday after Mass. I think we would have a lot more knowledgable and committed Catholics if we did. At the very least they would be able to defend our faith a lot better.