The LOTR trilogy is the most affecting set of films I've seen. I love every aspect of them. The plot is among the best you'll find in all of fiction, a tapestry of timeless human themes, each thread representing the life and experiences of a truly authentic character. The world is beautiful. Even the most unsavory places have a secret murky allure. And all of it, the story and setting and all they contain, is infused with and enriched by a truly robust and inventive lore. Peter Jackson gave Tolkien's vision extraordinary life. The actors inhabit their characters so fully as to become them. I cannot imagine any of the main or supporting roles filled by a different person. The set design is a marvel. Richard Taylor's design genius is on full display. It's as though WETA plucked objects straight from the ethers of imagination, fully resolved in flawless physical form. And of course the soundtrack, which is so sensitively, so expertly molded to the films that to remove it would be to strip away every scrap of emotional resonance, leaving a shadowless husk that retains none but the most vague hint of the series' cinematic power. Howard Shore is a man of exceptional musical talent, his contributions every bit as vital to LOTR as John Williams' are to Star Wars--perhaps more so.
The special features for all the extended editions offer essential insight into how special the production of these films was. Watching them I felt the greatest affection for the people whose daily efforts made possible the apparently impossible task of doing cinematic justice to Tolkien's work. I was also fascinated by the specifics of how they built the world of Middle Earth. For anyone who has even a passing curiosity about filmmaking, or the slightest interest in the LOTR films themselves, these features are a must see. Truly the best documentation of a film production I've ever had the pleasure of seeing, by a good mile.
Discussing a medium as rich and diverse as film, it doesn't make sense to nominate a single one (or trilogy, in this case) as the best without engaging in a long analytical process. What does "the best" mean, anyway? Displaying outstanding technical achievement? Rich in sophisticated narrative motifs? Personal favorite? Suffice it to say the Lord of the Rings trilogy is a masterpiece. I'm content to leave it at that.