What is the best library system in the United States?

Can you tell me what makes a library system in the United States stand out as the best? Are there specific criteria or features that define excellence? Perhaps it's the diversity of collections, the innovative use of technology, or the accessibility and convenience for patrons. I'm curious to learn about the specific libraries that have been recognized for their excellence and how they've achieved that status. Additionally, I'm interested in understanding the challenges that these library systems face and how they've adapted to overcome them. Can you provide some insights into the best practices and strategies that have contributed to their success?