In my experience:
I’ve met a lot of Eastern European political figures. My dad is friends with Martin Palous, the Czech ambassador to the UN. He is a hell of an interesting guy and has a lot of fascinating stories about the “velvet revolution,” or overthrow of the Communist government in 1989, which was actually influenced in large part - believe it or not - by punk rock. Adam Michnik visited our house in 1999 - a Polish dissident who spent years in jail, he fought against communism through his writing. Interesting stories, though he needed a translator because he didn’t speak English. I also met one of the top generals of the Indian Army - I can’t remember his name, but it was an interesting conversation. Among other things, he said that the problems between India and Pakistan are not as bad as people think. So I’d say that diplomats from exotic and faraway countries are rarely boring.
Cops, firemen, and military: usually friendly, easy to talk to and will share a lot of opinions on a lot of things, if they’re in a good mood and not tired or stressed out. I have friends in all the branches of the service - Air Force guys tend to be intellectual and driven, Marines sometimes cocky and reckless but dependable. My one friend who was in the Army had nothing but bad things to say about it, and wished he joined the Marines instead. The Navy guy I knew had the best stories by far. His tales of prostitution and other debauchery entertained me to no end.
Computer programmers: in my experience, they love to talk about computers and little else. YMMV.
Lawyers: They tend to talk mostly about cars, golf, sports or politics, but rarely have any good stories about their actual jobs. The one - ONE - exception to this rule, is a punk rock lawyer that I know who is covered in tattoos and mostly represents the punk and outlaw biker crowd. I talk to him regularly and he always has the most insane stories of unbridled criminality. He’s also insanely bitter and seems to hate the world.
High school teachers: a lot of my high school teachers were, by some coincidence, ex-military, and full of stories. Both my history teachers (European and American) were Captains in the cavalry during the first Gulf War.
Construction, road crew, traffic/street department, etc: lots of off-color banter conversations about drinking, drugs, pussy, fishing, and classic rock. A lot of raconteuring. Blue collar outdoor labor is one of the last strongholds of true storytelling.
Waitstaff (female): usually talk about trite and superficial stuff.
Waitstaff (male): will talk your goddamn ear off about their theater/music/political activism bullshit.