Cities with the most and least “scummy” casino games?

I don't think it is a matter of location. Poker is a game that involves money as a way of keeping score. As a result, it attracts people who are willing to push boundaries. Oftentimes deceptively (a polite way of saying cheating).

The bigger the game, the more likely there is someone looking to rig it. That is an eternal truth.

In other words, if HCL or LATB were filmed in NY, the results would be the same with just a different set of scumbags.

IMHO Las Vegas. Not because they are nicer or more honest but that the big money comes from getting the tourists in town not fleecing them at the poker table so the people in charge have a strong incentive to limit the more obvious forms of scum to keep the tourists happy.

I play sometimes in a relatively nice and well known Northeast poker room and across stakes there's definitely some mafia guys and gang members in these games, and some unsavory figures. It's well known Russian mafia has had a presence in the surrounding area and the room gets a good number of players from NYC and North Jersey so there's a lot of interesting characters. Before they installed metal detectors at entrance I'm pretty sure people were sometimes strapped in these games. But I've never really felt unsafe in the poker room, after all they likely aren't trying to start anything or bring unwanted attention to themselves. As to why they're playing, well that's their business.

I'm sure most poker rooms have at least some characters in the games.

Well LA is a pretty unique city with a lot of colorful characters, to say the least. So that shouldn't really surprise you one bit. But like the others have mentioned it will pretty much be the same all over the globe. Poker tends to attract the underworld so that's what you get to some extent. I would guess e.g. in a city like a Boston you would actually get a high % of peeps that have a kind of legitimate job. But it won't be 100% and just a wild guess. I wanted to play there once but the waitlist was too long.

Unless youre worried about getting angled or if someone just stole the money why would you care about someones background?

Because their background might give you some insight into whether or not you are getting angled or stolen from.

If you knew two people at the table were both members of the same drug cartel you wouldn't find it more likely they would collude with each other than two random people?

Nope, especially not for a low stakes game.