There is no "best" piece of evidence. For you must have at least two pieces of evidence for one to be best. The "truthers" have none. By evidence, I mean actual empirical evidence, not "evidence" derived from speculation based on ignorance of scientific principles and personal incredulity. Of course the collapse is going to look funny...to the uninformed. Of course the explanation isn't going to make sense...to the uneducated.
Ah, but there you have it. Yes, the best evidence troofers have is, in fact, no evidence at all. In Twooferdom, not only is it possible to prove a positive with a negative, it is strongly encouraged. Take this true conversation I had with teh troof at my local watering hole:
ME: (to an interested college) "So as the collapse initiated and the columns were pulled inward,..."
Troofer: (drunk and yelling from the opposite of the bar) "That's a load of ****, everyone knows the towers were brought down by thermite."
Me: "Really? I didn't know that. How so?
Troofer: "Man, Bush's cousin was in charge of security at the WTC. They brought in demolition crews and rigged the towers to blow the weekend before 9/11"
Me: "How could you possibly know this? Marvin Bush had a seat on the board of one of the many security contractors on the job at the WTC, by the way. He gave up that seat well before 9/11 too."
Troofer: "Why did they remove all of the evidence before before anyone could investigate it?" They shipped it all off to China so nobody would find the explosive residue!"
Me: "So where's your evidence that the evidence no longer exists and no forensic investigation was conducted?"
Troofer: "Evidence? Evidence? How do you explain the hole in the C ring at the pentagon? Hmmm? How do explain the total lack of airplane parts in Shanksville? Why did Siverstein say...."
Me: "Whoa, whoa, whoa. Hold up a minute, how 'bout answering my question; What is your evidence that there is no evidence?"
Troofer: "Dude, you suuuuuuuuuuuck! Total pwnage!"
Me: "Barkeep, I'll have a double."
Troofer: "So, what are you? NSA? FBI? CIA?"
Me: And keep'em coming.