I guess worst is subjective.
my current play-through (2nd attempt at this) I decided that I wanted to minimize dying, going for zero deaths of course but I know better than to expect that forever. Regardless, I find my first black forest crypt and start creeping around... and it has one of those go down a level ramps, and that had another go down a level ramp... and at the bottom it had MR. ** Rancid Remains. He poked me with a finger (presumably to see if I was fat enough to eat yet) and I fell over dead somewhere down there running away but poisoned too badly to make it. I came back to it much later and cleaned the place out (in that sense it had a lot of loot) but it was a rough start to the BF.

The swamp, you have small ones but there are always scrap piles. Its the forest ones that get me, the epic slog through the whole thing and you get like 1-2 cores if that, and some of those are large instances with tons of enemy and just don't have much loot. Then you go into some little one with 5 rooms and get 10. <random> is <random> I guess :)