It occurs to me that while I can't think of any great dialogue from I Claudius, it would be quite easy to write a recognisable parody of it. The same with Tinker Tailor Soldier Spy. What that probably means is that they were very good at being their own thing, even if that didn't involve a lot of memorable quipping.
For what it's worth I think there are certain types of dialogue that it's easy to make sound deep, and "manly men swap hard-won knowledge" is definitely one. A lot of dialogue is finding new ways for characters to express the same old ideas: "Don't trust flatterers", "Men are strong but easy to manipulate", "Tough things that last are worth more than fancy things that break" or whatever. I'm sure I've seen the sentiment "Sometimes, a good pair of boots is more useful than the works of Shakespeare" expressed a lot of times (after all, it's true), but never as well as that.
(Also, the dialogue in Game of Thrones (and perhaps I Claudius to a lesser extent) isn't quite modern dialogue, as it's in the slightly stilted, slightly Victorian style that for some reason many fantasy writers use.)
If I had to nominate a good line of dialogue, I'd go for "I refuse to join a club that would have me as a member" (possibly not the exact wording), which is funny but also expresses quite a complex idea in a striking and succinct way. Not that all dramas need to sound like the Marx Brothers, of course.