I grew up watching Butkus. He is IT for a middle linebacker. Total competitor, 100% every time and he hit like it was his life on the line. He bit an official's finger once when there was a pile for a fumble.
To tell you the truth, and I know this is going to make some folks mad, Url always seemed lackadaisical to me. I remember on press day before his only Superbowl appearance he said something about if they didnt win it was no big deal. I just never felt he had the same passion for the game as Butkus or Singletary. Seems to be the way players are today.
But Url was still one of the best, I just would put him after Butkus, Singletary.