I've always been impressed by the controllers in centers and TRACONs. They can have multiple frequencies they're monitoring in each ear, and no matter how polite we try to be we (pilots) have no way of knowing if we're stepping on a call on another frequency. They just have to deal with it. Not to mention communication amongst themselves to some extent as they hand people off, though I haven't been in a tower for a very long time, that may be automated/digital now.

And it's not like pilot/controller conversations are about weekend BBQ plans. It's as information dense as possible without sounding like a METAR report.