Tom's celebrity impersonations (Garrison Keillor, Howard Cosell, et al.)
JW's ability to hold a voice (I just listened to Troy Dershman again - it must have been killing him. I think his voices are underrated in general.)
Following up on both of these, Tom doing impressions of other people doing impressions or doing a character doing an impression of somebody is, in itself, impressive.
And the recent return of Pudge of how good the voice is there, and how easily Pudge can blend in with non-Newbridge callers at the start of a call if you don't know what you're listening for.
Silence.
Yes. I think the effective use of silence and pauses is one of those things that people realize least and probably takes time to appreciate for newer listeners and callers who want to jump in there instead of letting things develop. But it's a key to what makes Tom great as a storyteller and what makes the Best Show stand out as a live show where amazing topics and digressions can generate spontaneously.