This is a hell of a question. I really like the question a lot.
I listen to the 9 track demo more than any other demo that the band has. Either Untitled or Crawling. The band knew Untitled was next level... Crawling though sounds so different and unique to anything they had ever written at that point. I've posted about this before, but the 12 months after Chester joined the band might have spurned their most impressive music in their career. A Thousand Suns and Minutes to Midnight are both really impressive to me. ATS could be the most creative for sure.
But this 9 track demo is really wild. In the span of a year~ (we have them going in with Don in April or May 2000 I guess), they did the HTEP and all of these full band demos, but wrote all of this epic new music. Crawling, Untitled, Papercut, One Step Closer, Points, Super Xero, With You. Game changer songs, I mean just top of the top. Stuff like Rhinestone and Esaul existed since the Xero days, Pushing Me Away came much later when recording HT with Don, etc.
What they did at the end of 1999 and start of 2000 is really nuts to me. Some of the biggest songs of the past 20 years in music were written so quickly. Imagine having just the bombshell trio of Untitled, Crawling, and Plaster all written around the same time. So, so good. Crawling might be the most unique thing they wrote in that entire time period, though. To the point where they replicated the intro samples more times in their career (Numb, New Divide, Until It's Gone).