Which adventure map is considered the most difficult, and not due to fuel cans being further and further spread out?

By difficult I mean the toughest obstacles to traverse. Is it City? Or maybe Mines once you get to about 10k where the lava jumps get pretty tricky?

I feel like the maps where the challenge is just getting to fuel cans is boring and uninspired, like Forest for example. Same thing over and over, fuel cans spread further out. I know fuel cans are spread further for each map, but some have some pretty tough obstacles throughout.